Class IX Biology Book Chapter 02

English Sindh Text Book Board, Jamshoro.

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Chapter 2 STRUCTURAL ORGANIZATION OF LIFE

The cell is the basic unit of life. It is the smallest entity in which the life can exist. All the things that living organism can do are done by its cells. In fact some living things are made up of only one cell. Each cell gets food for energy, obtains oxygen, produces energy, gets rid of wastes, maintains homeostasis and produces new cells. How are all these life activities carried out? The answer can be found by examining the composition and working of its parts. Learning objectives:

Cell as a basic unit of living organism. Discovery of cell and cell theory. Concepts of light microscopy and electron microscopy. Microscopic and Ultramicroscopic structure of plant and animal cells. Structure and functions of different cell structures. Concept of Prokaryotic and Eukaryotic cells and their differences. Reproduction of cell, different methods. Mitosis and Meiosis and their significances. Three level of organization in living organism i.e. tissues, organs and system. Types of plant tissues, simple and compound tissues, their further

classification and function in different parts of plant body. Types of animal tissues, epithelial, connective, muscle and nervous tissues,

structure of these in relation to their function. Unicellular organization, Amoeba a unicellular organism. Multicellular organization. Brassica as multicellular organization, with root, stem, leaf, flower, fruit and

seed as their parts. Frog as multicellular organization with digestive, respiratory, circulatory,

excretory, nervous and reproductive organs and systems. Cell is as fundamental to biology as an atom is to chemistry. All organisms are made of cells, which behave as basic unit of their structure and function. The contraction of muscle cells moves your eyes as you read this book; when you decide to turn this page, nerve cells will transmit that decision from your brain to the muscle cells of your hand so every thing performed by organism is fundamentally occurring at the cellular level. 2.1 DISCOVERY OF CELL AND CELL THEORY In early classes we have studied that all living organisms are composed of cells. The question arises here how did biologist come to know that, obviously through observations. These observations started with the discovery of magnifying glasses and later on with the development of microscope. (Latin word micro = small; skopion = to see). In 1610 Galileo, an Italian astronomer and physicist developed microscope to observe small organisms. In 1665, Robert Hook made an improved microscope by combining lenses, called compound microscope and examined a slice of cork under it. He found small honey comb like chambers, which reminded him small rooms of monastery and are said cellula in Italian, so he also named these structures as cellulae or cell (small rooms). The cork was made from bark of oak, so he actually saw the cell-wall only. in 1842, Dutrochet, boiled plant material in nitric acid and then examined under microscope. It was found to consists of cells. In 1831, Robert Brown discovered a spherical body, the nucleus in the cells of orchids. Schleiden (1838) a German botanist, proposed that all plants are made up of cells. Next year another German Zoologist, Theoder Schwann stated that all animals are made up of cells. He



observed nuclei in all types of animal cells but failed to observe cell-wall in them. From here the difference between plant and animal cell started to establish. In 1858, Rudolf Virchow stated that new cells come only from other cells i.e animals cells come from animal cell and plant cells from plant cell. The combined efforts of Schleiden, Schwann and R.Virchow finally gave rise to cell theory. The salient features of the cell theory are as under: i) All living organisms are composed of one or more cells. ii) The cell is the smallest, basic structural and functional unit of all

organisms. iii) New cells are formed by the division of pre-existing cells. 2.2 LIGHT MICROSCOPY AND ELECTRON MICROSCOPY The evolution of biology as well as science often parallels the invention of instruments that extend human senses to new limits. The discovery and early study of cells progressed with the invention and improvement of visual instrument, like microscope. Microscopes of various types are still important tools for the study of cells.

Resolution Magnification Resolution is the capacity to separate adjacent objects.

Resolution is maintained upto certain magnification.

Resolution improves as the wave length of illumination become shorter.

Magnification is a means of increasing size of the object.

By increasing magnification resolution is disturbed.

Magnification improves with the focal length of lens.

The microscopes first used by scientist, as well as the microscope you use in the biology laboratory are light microscopes. These microscope use visible light as the source of illumination and glass lenses for magnification. These lenses reflect the light in a way that the image of the specimen is magnified as it is projected into the human eye. The light microscope can magnify the object upto 1000 times but its resolving power is very limited, i.e just 0.2µm (Resolving power is a measure of the clarity of the image). In 1935, a new type of power full microscope called Electron microscope was invented by scientist to improve the resolving power of microscope. It uses a beam of electron as a source of illumination. The electron beam increases its resolving power. Modern electron microscope can achieve a resolution of about 0.2 nm, a thousand times improvement over light microscope. The electron microscope uses electromagnet as lenses instead of glass lenses. This image cannot focus in human eye, therefore screen or photographic plates are used to review and focus these images.

Units of measurement 1 centimeter (cm) = 10-2 meter. 1 millimeter (mm) - 10-3 meter. 1 micrometer (µm) =10-6 meter. 1 nanometer (nm) = 10-9 meter.

Electron microscopes reveals many organelles that are impossible to be seen with the light microscope. But the light microscope has many advantages especially for the study of live cells. In electron microscopy, chemicals and physical methods are used to prepare sample which kills cells.



2.3 BASIC STRUCTURE OF CELL Cells are of different shapes and size according to their functions. inspite of variation found in their shape, all cells basically share many structures in common like cell membrane, cytoplasm, nucleus, etc. In plant cell, cell-membrane is surrounded by a cell-wall. 2.3.1 Cell - Structural and Functional unit: Microscopic studies reveal that all living organisms are composed of cells. Therefore, cell is a unit of structure of living organisms. Cells are of different shapes and sizes, as they have to perform different functions. All basic functional activities, characteristic of living things, occur in the cell. Therefore, cell is also a unit of function of all living organisms. 1. Cell-wall: Cell-wall is the non living, outermost boundary of plant cells, bacterial cells and fungal cells. It is not found in animal cell. It is secreted by the protoplasm of the plant cell. In plant cell it is mainly composed of cellulose and pectin. Ultra microscopic structure of cell-wall shows that cellulose make the fibers which are arranged in criss cross manner. These fibers are kept in their position by a cementing material called calcium pectate (Pectin). Bacterial cell-wall is made up of protein and carbohydrate while fungal cell wall is made up of fungal cellulose and chitin. Thickness of cell-wall varies in different cells of plant. It is composed of three main layers: middle lamella, primary wall, secondary wall and some times tertiary wall. Middle lamella is formed between the primary walls of neighbouring cells. Primary wall, the first wall of plant cell is chemically composed of cellulose and pectin, some limes, lignin. Cell-wall provides protection and support to the cell. It gives a definite shape to the cell. It also performs the function of transport of material from outside to inside or vice versa, therefore, it is permeable in nature. 2. Cell- membrane: The cell-membrane or plasma membrane surrounds nucleus and cytoplasm in all types of cells. However in bacteria and plants, plasma membrane itself is surrounded by a cell-wall. It can repair itself to some extent. Different models have been presented to understand the structure of cell membrane. The most acceptable model among them is Fluid mosaic model presented by Singer and Nicholson (1972). According to it, cell membrane consists of lipid (Phospho-lipid) bilayer, in which protein molecules float like iceberg in the sea. This basic structure is found in all the membranes of mitochondria, chloroplast etc. Therefore, it is also called unit membrane. Cell membrane is a selectively permeable membrane because it regulates selective movement of molecules. In many animal cells the cell membrane infolds, taking in materials in the form of vacuoles. This process is called endocytosis. 3. Nucleus or Karyon: Nucleus (discovered by Robert Brown in 1831) is an important arid prominent structure present inside the cell. It controls all the activities of cell. It may be spherical or irregular in shape. In animal cell it is usually present in the center but in plant cell, due to presence of large vacuole it is pushed towards cell-membrane. Nucleus is enveloped by a double membrane called nuclear- membrane. This membrane possesses large number of nuclear pores. Nucleus is filled with a gel like substance called nucleoplasm. The nucleoplasm contains nucleoli and a network of thread like structures called chromatin network. The threads of chromatin become prominent during cell-division. Each thread is called chromosome. These structures of major importance. They are composed of Deoxyribo nucleic acid (DNA) and protein. DNA plays significant role in the



inheritance of characters as well as in controlling or regulating the cell activities. The number of chromosomes in the cells of all individual of the same species always remains constant.

Cells of organism No. of Chromosomes Man 46 Frog 26

Chimpanzee 48 Drosophila (fruit fly) 08

Onion 16 Potato 48

Garden pea 14 4. Cytoplasm: It is the translucent fluid portion of the cell lying in between plasma membrane and nucleus. It consists of an aqueous ground substance called cytosol and granular portion called cytoplasmic organelles. Chemically cytoplasm is about 90% water and forms a solution and serves as store house of vital chemicals. It is a site of metabolic reactions like protein synthesis, glycolysis etc. Many reactions can occur at the same time in different regions of the cytoplasm. Some important cytoplasmic organelles found in eukaryotic cells. 1. Endoplasmic reticulum 2. Golgi complex 3. Mitochondria 4. Plastids 5. Centrioles 6. Ribosomes 7. Vacuoles 1. Endoplasmic reticulum: (Endo= inside, plasma = protoplasm, reticulum=net work). It is a network of membranous channels or tubules extending throughout the cytoplasm. The channels seem to be in contact with plasma membrane as well as nuclear membrane. There are two types of endoplasmic reticulum. i) Rough endoplasmic reticulum having ribosomes at its outer surface which

are involved in protein synthesis. ii) Smooth endoplasmic reticulum without ribosome. Endoplasmic reticulum plays important role in the synthesis and transport of material within the cell. It also provides mechanical support to the cell so that its shape is maintained. It detoxifies the harmful effects of drugs. 2. Golgi complex: They were discovered by Camillo Golgi and thus called Golgi complex or bodies or apparatus". They are set of smooth membranes that are stacked into flattened, fluid filled sacs or vesicles containing carbohydrate, glycoproteins and enzymes. Golgi bodies are mainly concerned with the cell secretions. 3. Mitochondria (Sing; mitochondrion): They are generally rod-like or bean shaped organelles consisting of double membrane. The inner membrane is folded. These infoldings are called cristae while the fluid present inside is called matrix. Mitochondria contain enzymes which break the food for the production of energy. As producers of energy they are called Power house of the cell. The number of mitochondria in cell relates to its activities. 4. Plastids:



Plastids are found in the cells of all the higher plants. These are the organelles which contain different types of pigments. Plastids are of three types on the basis of their pigment or colour (Fig: 2.11) i) Chloroplasts have green pigment i.e. chlorophyll found in leaves and

other green parts of a plant. They manufacture carbohydrates by the process of photosynthesis.

ii) Chromoplast have coloured pigments other than green found in fruit, flower, petals and other coloured parts of plants .

iii) Leucoplast (leucos = white or colourless) are colourless, found in the cells of underground parts of plants. They store food in the form of starch.

5. Centrosome and Centrioles: A rounded structure, the centrosome is present near the nucleus in animal cells. A centrosome contains two centrioles (Fig: 2.12). Each centriole consists of a cylindrical array of 9 rows of microtubules. They form fibrous protein spindle which help in movement of chromosomes towards poles during animal cell division. 6. Ribosome: They are granules, rich in ribonucleic acid (RNA). They serve as sites where proteins are synthesized hence called protein factories of cell. They are found free in cytoplasm as well as attached on the surface of rough endoplasmic reticulum. 7. Vacuole: They are the fluid (other than cytoplasm) filled sacs surrounded by a membrane called tonoplast. In animal cell they are numerous, small but temporary structures while in plant cell they are permanent and very large in size, one or a few in number. They are concerned with storage of cell sap. 2.4 PROKARYOTIC AND EUKARYOTIC CELL There are two types of cells, Prokaryotic and eukaryotic cells. Prokaryotes have prokaryotic cell while eukaryotes have eukaryotic cells. Prokaryotic (pro: before; karyon: nucleus) cell does not possess true nucleus. It means its nuclear material is not enclosed in a proper nuclear membrane. These types of cells are found in bacteria and cyanobacteria (blue green algae). Such organisms are called prokaryotic organisms. Eukaryotic (eu: true, karyon: nucleus) cell possesses proper nucleus where nuclear material is enclosed in a proper nuclear membrane. Plants and animals are composed of this type of cells and are called eukaryotic organisms. Followings are the differences found between them.

Prokaryotic cell Eukaryotic cell 1. Nuclear membrane is absent

therefore prokaryotic cells do not possess distinct nucleus.

2. They do not have many of the membrane bound structures e.g. mitochondria E.R, Golgi apparatus etc.

3. Ribosomes are of small size and freely scattered in cytoplasm.

4. Nucleoplasm is absent. 5. Single chromosome is found. 6. Respiratory enzymes are located on

the inner surface of the cell

1. A double nuclear membrane is present. They have well defined nucleus.

2. They have membrane bounded structures (organelles).

3. Ribosomes are of large size and present either on endoplasmic reticulum or free in cytoplasm.

4. Nucleoplasm is present 5. Proper chromosomes in diploid

numbers are present. 6. Respiratory enzymes are



membrane. 7. These cells are simple and

comparatively smaller in size i.e. average 0.5 -l0nm in diameter.

8. Bacteria and cyanobacteria are examples of prokaryotes.

present in mitochondria. 7. These cells are complex and

comparatively larger in size i.e. 10- l00nm in diameter average.

8. Fungi, algae, animal and plants are examples of eukaryotes.

2.5 CELL DIVISION Cells reproduce and increase in number by division. After growing to a certain maximum size, a cell may undergo the process of cell division. During this process the nucleus divides first. This is followed by division of the cytoplasm. This nuclear division is called Karyokinesis (karyon=nucleus; kinesis = division) while the cytoplasmic division is called Cytokinesis. Thus two daughter cells arise from a single division of a cell. There are two main types of cell division found in living organisms. (1) Mitosis (2) Meiosis 1. Mitosis: In this type of cell division a parent cell divides into two daughter cells in a way that the number of chromosomes in the daughter cells remains the same as in the parent cell. Although mitosis is a continuous process, its karyokinesis can be divided for convenience into four phases which are Prophase, Metaphase, Anaphase and Telophase. Let us now study mitosis is an animal cell.

i) Prophase: During early prophase chromatin material condenses and becomes visible as thick coiled, thread like structures called chromosomes. Each chromosome at this stage is already double, i.e. consists of two chromatids. The chromatids are attached to each other at centromere. The nuclear membrane gradually disappears and at the same time centrosome divides to form two centrioles, each moves towards the opposite pole of the cell and forms the spindle fibres. The centrioles are absent in plant cells.

ii) Metaphase: During this phase each chromosome arranges itself on the equator of the spindle. Each chromosome is attached to separate spindle fibre by its centromere.

iii) Anaphase: In this phase the centromere of a chromosome divides and the chromatids of each chromosome separates from each other and begin to move towards opposite poles. In this way one set of the chromatids (each chromatid is now an independent chromosome) move towards one pole while the other set towards the other pole.

iv) Telophase: This is a stage when the chromatids (now called chromosomes) reach the poles and their movement ceases. Each pole receives the same number of chromosomes as were present in the parent cell. The nuclear membrane is reformed around each set of chromosomes. In this way two daughter nuclei are formed in each cell. Soon the cytoplasm of the cell also divides and two daughter cells arise. The nucleus of each daughter cell contains the same



chromosome number as in their parent cell. In this way the daughter cells are exact copies of their parent cell.

Significance of mitosis: Mitosis plays an important role in the life of an organism. It is responsible for development and growth of organisms by increasing exact copies of cells. With few exceptions all kinds of asexual reproduction and vegetative propagation take place by mitosis. The production of new somatic cells, such as blood cells depends on mitosis. The healing of wounds, repair of wear and tear within organism is also dependent upon the mitotic division. 2. Meiosis: Meiosis or reduction cell-division is a special type of cell-division S| which a parent cell finally divides into four daughter cells in a way that the number of chromosome in each daughter cell reduce to half of their parent cell. Thus it is the reduction of the diploid (2n) number of chromosomes to the haploid (n) number. In animals meiosis produces gametes (sperms and eggs) while in plants it gives rise to spores. The process of meiosis involves two consecutive divisions. (a) Meiosis I - First meiotic division or reduction phase (b) Meiosis II - Second meiotic division or meiotic mitotic phase (a) Meiosis I - First meiotic division or Reduction Phase: This division consists of the following phases.

i) Prophase I: Those chromosomes in the cell which 'are similar to each other in shape and size are called homologous chromosomes. Homologous chromosomes occur in pairs. The difference between mitosis and meiosis starts at this point. In mitosis individual chromosomes remain separate from each other while in meiosis the homologous chromosomes come together and form pairs. In each homologous pair, there are four chromatids, since each member (chromosome) of the pair has already doubled itself. Homologous chromosomes join to exchange their parts at certain places. This exchange is called crossing over. During crossing over exchange of genetic material takes place and new combination of genes result. The nuclear membrane disappears and at the same time spindle fibres are formed.

ii) Metaphase I: During this phase pairs of homologous chromosomes arrange themselves on the equator of the spindle. Unlike mitosis, it is the homologous pair and not the individual chromosomes which attach at separate fibre of the spindle.

iii) Anaphase I: The members of the homologous pairs now begin to separate and move towards the opposite poles.

iv) Telophase I: In this phase the chromosomes come to rest at the poles. The nuclear membranes are reformed around each set of chromosomes resulting in formation of two daughter nuclei. On completion of nuclear division, the cytoplasm also divides and two daughter cells are formed. Each daughter cell has half (haploid) the number of chromosomes present in the parent cell (compared with the cell in prophase) .Thus, the first meiotic division reduces the 2n (diploid-2 sets) chromosomes to n (haploid-half or one set).

(b) Meiosis II - Second meiotic division or Equational Division: During second meiotic division the details are almost similar to those seen in mitosis. During prophase, spindles are formed and the nuclear membrane



disappears. In metaphase, the chromosomes (each consisting of two chromatids) arrange themselves on the equator. Their chromatids separate from each other in anaphase and migrate to the opposite poles. In telophase, the nuclear membrane reappears around each set of chromatids (now called chromosomes) and the cytoplasm divides forming two daughter cells. So at the end of meiosis four daughter cells are produced in total, each possessing a haploid nucleus. Thus meiosis produces cells (gametes or spores) with a haploid number of chromosomes. Significance of meiosis: Meiosis plays very important role in keeping chromosome number constant in a species from generation to generation. When the haploid male gamete (sperm) fertilizes i.e. fuses with the haploid female gamete (ovum) to form a zygote, the diploid number of chromosomes is restored (n + n = 2n). Meiosis is responsible for genetic variability i.e. the individuals of a given species differ from one another. It is due to crossing over which takes place during prophase I. This genetic variability provides the basis of evolution by providing raw material for it. 2.6 ORGANIZATION OP CELLS TO FORM TISSUES, ORGANS AND ORGAN SYSTEM So far you have learnt about the cell as the basic structural and functional unit of life. The question now is how can a cell express itself as an independent living thing? You know that some small organisms (Amoeba) are made of only one cell These organisms are called unicellular organisms. They represent single cells capable of independent existence by making use of their organelles. Once capable of independent existence, the cell has become an organism. Such an organism represents the unicellular level of organization of life. In some cases, cells have come together to form loose assemblies and live together as a colony. In others, cell with similar structure and function have formed groups. Both have laid down the foundation of multicellular level of organization of life. 2.6.1 Tissues: A major step in the direction of multicellular organization of life has been the formation of tissues. A tissue consists of a group of cells which are similar in structure and function. Both plants and animals tissues have achieved increasing complexity by formation of organs and organ systems. 1. Plant tissues: In plants there are two basic types of tissues which are as follows.

i) Meristematic tissue: This tissue contains cells which have ability to divide, so that the number of cells increases and the organism can grow . Meristematic cells are smaller in size with comparatively thin walls and a nucleus in the center. This tissue is commonly present in root tips and shoot apex and helps to increase the length of the root and the shoot by adding primary tissue. ii) Permanent tissue: Permanent tissue is formed from meristematic cells. This tissue is different from meristematic tissue because its cells do not divide. The walls of these cells are thick enabling them to maintain their shape. Permanent tissue may be classified into two groups i.e. simple tissue and complex tissue. Simple tissue is made up of one type of cells forming a homogeneous or uniform mass and a complex tissue is made up of more than one type of cells working together as a unit.

a) Simple tissue: Simple tissues may further be divided into following type on the basis of their structure, i.e. Parenchyma, Collenchyma and Sclerenchyma.



i. Parenchyma: It consists of living cells which are more or less equally expanded on all sides. These cells have intercellular spaces. They are present in all the soft parts of plant. It is food storing tissue.

ii. Collenchyma: It consists of some what elongated cells with the corners filled with cellulose and pectin. Collenchyma occurs in a few layers under the epidermis of herbaceous dicotyledons.

iii. Sclerenchyma: Sclerenchyma (scleros =hard) consist of very long, narrow thick walled and lignified cells. They are dead cells. They become hard by deposition of chemical like lignin and thus provide support to the plants. They are found in xylem and hard fruit coats etc.

b) Complex or Compound tissues: Compound tissues are mainly of two types: (a) Xylem (b) Phloem. These will be discussed later under conducting tissues.

Types of permanent tissues on the basis of function:

i) Epidermal tissues: The cells of these tissues are rectangular in shape. These tissues form the outer layer of root, stem and leaf .The cells in it are very compactly arranged so that there is no space between them. However, in the stem and leaves, pores called stomata are present through which gases are exchanged. These tissues protect the inner parts of plant.

ii) Ground tissues: Ground tissues are composed of thin walled parenchymatous cells, which axe formed from meristematic tissue. These cells are basically meant for storing food. These tissues are present in all parts of the plant except the epidermal and the vascular tissues.

iii) Supporting tissues: When cells reach a maximum size their cell wails become thick due to deposition of special material and become dead. Such cells make up supporting tissue. This tissue is of various shapes and provides rigidity and support to the plant. Sclerenchyma (thick walled, lignified and elongated) and collenchyma (living cells with thick cellular walls with few small intercellular spaces) are examples of the supporting tissues.

iv) Conducting or Vascular tissues: These tissues consist of elongated cells with thick or thin walls. Xylem and Phloem are examples of this tissue. The xylem consists of sclerenchyma vessels and fibers, which conducts water and salts from the soil to the leaves and also provides support. The phloem is made up of living cells like sieve tubes, which conducts food from leaves to various parts of the plants. Xylem and phloem together form vascular bundle in the stem while they remain separate from each other in the roots.

2. Animal tissues: Like plants, animals have tissues which form organs and organ system. Some important types of animal tissues are: i) Epithelial tissue: The cells of this tissue occur in a single layer and are

closely packed together. This tissue forms surface layer under lines of the tubular organs of the body. Epithelial tissue occurs in glands where it is variously folded.

ii) Connective tissues: These tissues provide support to other tissues and organs and bind them together. They consist of a ground substance, cells and fibres. They range from soft to very hard tissues. Fatty tissues are examples of the soft type. Cartilage and bone are special types of these tissues and are hard. Blood is also a special connective tissue with cells suspended in a fluid medium. It transports materials in the body.



iii) Muscular tissues: This tissue is formed of muscle fibres. Each muscle fibre is an elongated cell, which has the ability to contract and relax. These tissues are responsible for movement of the body and body parts.

iv) Nervous tissues: These tissues are formed of cells called neurons or nerve cells. Nerve cells are specialized to conduct messages in the form of electrical currents. The nervous system (brain, spinal cord, nerves) is made up of this tissue. '

2.6.2 Organs: Your arm is an organ because it consists of various kinds of tissues such as epithelial tissue, muscular tissue, connective tissue and nervous tissue. All of these tissues have come together in the arm to make it an organ. Your heart, kidney, liver and many others structures are organs made in the same way. Similarly, in a plant the root, the stem and the leaves arc organs. The stem, for example, consists of several tissues such as epidermal tissue, ground tissue and conducting tissue. 2.6.3 Organ systems: Organs work together as a unit to perform a particular function to make an organ system. For example, the digestive system is made of organs such as mouth, gut, liver and pancreas are all working together to digest food. There are other systems in the animal body such as transport, respiratory, excretory, muscle, skeletal, nervous and reproductive systems. In plants also, the tissues and organs (root, stem, and leaves) are organized to form systems. However, the systems, here are not so clearly organized as in the animals. It is usual to study these in plants, as conduction, storage, supporting systems, or root and shoot systems. In this chapter you are studying life at various levels of organization from the simplest to the most complex. A simple diagram of this organization is given below: Cells Tissues Organs Systems Organism 2.7 UNICELLULAR ORGANISMS Those animals and plants, which are single-celled, are called unicellular organisms. Amoeba is one of the example. Amoeba: It is a unicellular aquatic organism found in stagnant water pools and ponds. It is microscopic in size measuring about 0.25 millimeter. It does not possess a permanent form and' keeps on changing its shape. The structure of Amoeba is very simple. The nucleus and cytoplasm are surrounded by a protective cell membrane. Cytoplasm is differentiated into two parts. Its outer portion, which is clear and transparent is called ectoplasm. The inner viscous, translucent and granular part is called endoplasm. The endoplasm contains many food vacuoles of different size, a contractile vacuole and other cells organelles. Nucleus is usually present in the centre but as the Amoeba moves, the nucleus changes its position. The contractile vacuole functions to remove excess water from the body. The food vacuoles contain food particles. The animal moves by producing temporary finger-like projections called pseudopodia (Pseudo = false, podia a feet). The pseudopodia are also used to capture food particles, which enter the body as food vacuoles. Amoeba respires by exchanging gases with the surrounding water through its surface. 2.8 MULTICELLULARORGANISMS



The majority of living organisms consist of many cells and are called multicellular organisms. Brassica and frog have been selected here as representative examples of multicellular plants and animals, respectively. 2.8.1 Brassica: Brassica campestris is the botanical name of mustard (sarsoun). You are very familiar with this plant since its oil (mustard oil) is used for cooking and its leaves are used as vegetable (saag). Structure of Brassica: This plant consists of roots, stem, leaves, flowers, fruit and seeds. These parts can be divided into two categories on functional basis i.e. vegetative parts and reproductive parts. The vegetative parts are those which do not directly take part in sexual reproduction. These parts are root, stem, branches and leaves. The reproductive parts consist of sex organs which are directly related to sexual reproduction. These are flowers. 1. Vegetative parts:

i) Root: The root is that part, which grows under the soil and develops from the radicle of the seed. The first part of the root to arise from the radicle is known as the primary root. During its growth it gives off secondary and tertiary roots. The primary roots are thicker than the secondary and tertiary roots. The tips of all the roots bear a cap, the root cap. The root bears fine, thin root hairs. The plant absorbs water and minerals from the soil through the root hairs only, the rest of the root fix the plant to the soil.

Internal structure: The outer part of a root is the epidermis (epi=above; derma=skin), which protects the root. Root hairs are outgrowths of epidermal cells. Next to epidermis is the cortex. Cortex is composed of parenchyma cells. Parenchyma cells store food material. Within the cortex is a central cylinder region called the stele. The stele of the root is surrounded on the outside by a layer of cells called endodermis. Next to the endodermis is a layer of cells called pericycle. Branch of the root originate from the pericycle. The central part of the stele is occupied by a star shaped xylem. In between the arms of the xylem is phloem. Rest of the stele is made of parenchyma cells.

ii) Stem: This part of plant develops from the plumule of the seed and grows away from the soil. It bears branches and flowers. The point, on the stem or on a branch, which gives rise to leaf, is known as the node. The part between two adjacent nodes is called the internode. The stem and the branches transport water and salts from the root to the leaves. It also transports prepared food from the leaves to all parts of the plant. In addition, the stem supports the leaves and the branches in the air, thus enabling the leaves to receive maximum amount of sun light for photosynthesis. The stem and its branches also bear flowers, which are the reproductive organs.

Internal structure: A cross section of Brassica stem shows that it is surrounded on the outside by a single layered epidermis. Next to the epidermis is cortex. The cortex is made up of parenchyma and collenchyma cells. Food material is stored in the cortex. Next to the cortex is a ring of vascular bundles. Each bundle consists of xylem and phloem. Xylem is located towards the inside and phloem towards the outside. In between xylem and phloem, there is a region consisting of meristematic cells



called cambium. The centre of the stem is occupied by pith. It is made up of parenchyma cells and stores food material.

iii) Leaf: Leaves grow out on the stem and its branches from the nodes. Generally, the leaf of Brassica consists of two parts. The lower stalk like part is the petiole and upper green expanded portion is the lamina. Young leaves are without petioles and their margins are entire or smooth but in mature leaves the margin is wavy. There is a swollen vein in the middle of the leaf which is known as midrib. The branch veins emerge and spread in the leaf like a net. These veins are actually vascular bundles consisting of xylem and phloem. This network of veins supports the leaf and keeps its lamina in an expanded position. New branches of the plant arise from buds present in the axil of the leaf. The function of the leaf is to prepare food. Therefore, all of its tissues are arranged in such a way that photosynthesis can take place easily.----------------------------------------- The leaves are arranged on the stem and branches in such a way that their upper surfaces remain directly exposed to sunlight while the lower surface does not get the same amount of light. Due to this difference the upper and lower surfaces are slightly different from each other. Leaves having different upper and lower surfaces are called bifacial leaves.

Internal structure: A leaf is composed of several distinct cell layers. The upper layer of a leaf is called the upper epidermis. The lower layer of the leaf is called the lower epidermis, which contains stomata (Sing: Stoma). Each stoma has a pore and two guard cells. The tissue between upper and lower epidermis is called the mesophyll. The mesophyll cells below the upper epidermis are longer than broad and are closely packed. It is called the palisade layer. The cells next to the palisade layer are irregular in shape and loosely arranged having spaces like sponge and is called the spongy layer. Photosynthesis takes place in palisade and spongy mesophylls. Running through the leaf are many vascular bundles or veins. The veins are composed of xylem and phloem. Xylem is located towards the upper side and the phloem towards the lower epidermis. 2. Reproductive parts Flower: With growing age, Brassica plant bears small, yellowish flowers. Flowers are the most beautiful and important parts of the plant. They are arranged on young branches in a special way. This special arrangement of the flowers on the stem is called inflorescence. Parts of the flower: The flower in Brassica is situated on a stalk known as pedicel. The tip of the pedicel bears thalamus. The floral leaves are arranged in four whorls on the thalamus. These whorls, starting from the outermost to the central one, are in the following order. i) Calyx: This is the outermost whorl and consists of four free sepals. The

sepals are light greenish in young flowers but as the flower matures, their colour also becomes yellowish like that of the petals. The most important function of the calyx is to cover the inner parts of the flower and to protect them from sunlight and rain.

ii) Corolla: This is the second whorl and is composed of four free yellow petals. Because of the petals, the flower becomes very conspicuous that honey bees, butterflies and other insects are easily attracted and thus help in pollination.



iii) Androecium: The androecium lies inside the petals. It makes the third whorl of the floral leaves. Its parts are not leaf-like. The androecium consists of six free stamens which are the male reproductive organs of the flower. In Brassica flower, the stamens are arranged in two circles. The outer circle has two small stamens. The inner circle has four long stamens. Each stamen has two well defined parts, a lower delicate stalk called the filament and an upper swollen part called the anther. Each anther contains numerous pollen grains. When the anther matures a longitudinal slit in its wall enables the pollen grains to escape. There are dark green nectaries of small size at the base of the androecium. These nectaries contain nectar (a honey-like substance). This nectar is the food of insects. When the insects are attracted towards the flowers to collect this nectar pollen grains get attached to their bodies and are transferred from one flower to another. This results in the pollination of flowers.

iv) Gynoecium: This is fourth whorl occupying the central position in the flower. The parts of the gynoecium are called carpels, who are the female reproductive organs of the plant. In Brassica, gynoecium is formed by the union of two carpels. Each carpel is divisible into three main parts. The lower swollen part is the ovary. Above the ovary carpel extends into a thin stalk, the style. The style has swollen tip, which is called stigma. In the ovary many ovules are present, which ripen into seeds. The ovary ripens and is converted into fruit. The fruit of Brassica is a long dry capsule with many seeds. The seeds are very small and light. They can be easily dispersed by air currents. When these seeds fall on a suitable place they germinate and produce new Brassica plants.

2.8.2 Frog: The frog lives both in water as well as on land. It swims in water and moves by jumping when on land. There is a membranous skin between its toes which helps in swimming. There are five toes in each foot but the hand has only four fingers because the thumb is rudimentary. In male frog the first finger is thicker than the others. Frog has neither a neck nor a tail. As the head is directly attached to the trunk frog cannot move it as we can. The conical head has two large bulging eyes. Behind each eye is a circular area called tympanic membrane. These membranes help in hearing. At the tip of the snout it has two openings called external nostrils by which frog breathes. The skin of the frog is loose and slippery. It is slippery due to secretions produced by glands present in it. Frogs are found in abundance in the rainy season during which they lay eggs. They hibernate during the winter season by burying themselves in the mud and stay there throughout the winter. This phenomenon is called hibernation or winter sleep. Internal organs: The internal organs are located in the body cavity, which is also called coelom. These organs make up various systems, which perform specific functions. These are as follows: 1. Digestive system: The organs involved in the breakdown of complex food

into simpler form (digestion) constitute the digestive system. This system is composed of a tube, the alimentary canal and special glands associated with it. The alimentary canal consists of buccal cavity, pharynx, oesophagus, stomach and intestine. i) Buccal cavity: Food enters into the buccal cavity through mouth.

The upper jaw has a row of weak but pointed teeth. They are not meant for chewing food but prevent it from slipping out of the mouth. The tongue of frog is unique in being attached in front to the floor of



the buccal cavity and being free behind. This allows the animal to throw it outward.---------------------------------------------------------- Frog feeds mainly on insects. On seeing the prey, it suddenly throws out its tongue. The prey sticks to its sticky tongue. The tongue is then immediately withdrawn and the prey is swallowed.

ii) Pharynx: The buccal cavity opens into a short but narrow pharynx, which leads into a wide tube,, the oesophagus. Immediately behind the tongue on the floor of the pharynx is a slit like opening, the glottis, which opens into the lungs. When the food passes into the oesophagus, the glottis is closed and during respiration it is opened.

iii) Oesophagus and stomach: Pharynx opens into a wide tube called oesophagus or gullet; It transports food into the stomach. Stomach is a thick walled, muscular and glandular sac. Anterior end of stomach is called cardiac end while posterior end is called pyloric end. Food is grounded in stomach and mixed with enzyme pepsin, which partially digest proteins. Food in stomach changes into a paste like substance called chyme.

iv) Intestine: The intestine is a long narrow coiled tube. It is divisible into small and a large intestine. The partially digested food from the stomach enters the small intestine through pyloric end, where its digestion is completed. The digested food is absorbed into blood. The undigestible parts of the food enter the large intestine, also called rectum. The short terminal part of rectum is called cloaca. From cloaca undigested food is expelled out as faeces through its opening called cloacal aperture. This is a common aperture for urine, reproductive and undigested food discharge.

v) Liver and pancreas: The liver is a large reddish-brown gland located adjacent to the stomach. Its secretion is known as bile. Between the lobes of the liver is a rounded pouch called gall bladder, which stores bile. A bile duct arises from it. On its way, this duct passes through pancreas and joins the pancreatic duct. The pancreas lies between stomach and duodenum, the first part of small intestine. Its secretion, pancreatic juice, is carried by the pancreatic duct. The pancreatic duct and the bile duct join to form a common hepato-pancreatic duct, which then opens into duodenum. The bile and the pancreatic juice help in the complete digestion of the food in the small intestine.-------------------------------------------- Digestion is a process by which the complex insoluble food substances are converted into soluble form by the action of enzymes. The digested food is then absorbed into the blood through the intestinal walls.

2. Respiratory system: Energy is required by every organism to carry on all the life activities. It is produced by the oxidation of food specially glucose. This process takes place in the cells. For oxidation the cells require oxygen and as a result of oxidation of food they produce CO2 as waste product. This entire process called respiration, divided into two phases. a) Gaseous exchange or Extra-cellular respiration b) Cellular respiration. We will restrict our discussion upto gaseous exchange as respiration. Frog has three types of respiration on the basis of organs involved in the gaseous exchange. These are: i) Pulmonary respiration



ii) Cutaneous respiration ii) Buccal respiration i) Pulmonary respiration:----------------------------------------------------

The gaseous exchange, which takes place in lungs is called pulmonary respiration. The frog has two lungs, which are balloon like structures. Their outer surface is smooth but their inner surface has numerous folds which increase the area for gaseous exchange. The lungs are richly supplied with blood vessels. Each lung has a bronchus at its upper end. The two bronchi open into a larynx. The glottis opens into the larynx.------------------------- During respiration air is taken in by the external nostrils. It passes into the buccal cavity through the internal nostrils. From here it enters the glottis, passes through the larynx and bronchi finally reach the lungs. In the lungs, exchange of gases between air and blood takes place i.e. oxygen is taken up by the blood and CO2 is given out, which leaves the body through same route. Aresting human breathes out about 500 litres of CO2 every 24 hours.

ii) Cutaneous respiration:----------------------------------------------------Gaseous exchange carried out by skin, is called cutaneous respiration. Frog uses skin as a respiratory organ during swimming and hibernation. Oxygen diffuse into blood through skin while CO2 diffuses out from the network blood capillaries in skin.

iii) Buccal respiration:---------------------------------------------------------The lining of buccal cavity is thin, moist and richly supplied with blood capillaries. Here also exchange of gases takes place between the air and blood. This type of respiration is called buccal respiration.

3. Circulatory system: Every cell requires a supply of oxygen and nutrient molecules and must get rid of waste products. For this purpose a transport system usually called circulatory system is required. Blood transports these materials during its circulation through out the body. Frog has a closed type circulatory system in which blood circulates in the closed circuit of blood vessels being pumped by an organ called heart, This system is also called cardiovascular system. It consists of: i) Heart- strong muscular pumping organ. ii) Three kinds of blood vessels:

(a) Arteries － Which carry blood away from heart. (b) Veins － Which return blood to the heart. (c) Capillaries － Exchange material between tissues and blood.

Heart: Heart is a conical, muscular pumping organ, located in the anterior region of body cavity. It is enclosed in a membrane called pericardium. It contracts and expands continuously through out the life. This contraction and expansion of heart is called heart beat, due to which blood circulates continuously in the body. Frog heart consists of three chambers.

(i) Right auricle or Atrium. (ii) Left auricle or Atrium. (iii) Ventricle.

The longest heart stoppage was 4 hours. A Norwegian fell into the sea in December 1987.



Survival was due to the low temperature of his body in the sea. The truncus arteriosus originates from ventral side of the ventricle and divide into two branches each of which divides into three arches (arteries). Another thin walled triangular sac called sinus venosus formed by major veins opens into right atrium. Both of these structures are not true chambers of heart but often called accessory chambers. In heart, the flow of blood is continuous and moves in two path ways. The oxygenated blood from the lungs enters the left auricle through pulmonary veins. The deoxygenated blood from all other parts of the body enters the sinus venosus. From sinus venosus, it reaches the right auricle. When the two auricles contract, the blood is pushed into the single ventricle. When ventricle contracts it is pumped into the truncus arteriosus From here it enter (a) the pulmonary arteries, which carry the blood to lungs for oxygenation and (b) the systemic arteries, which supply it to all parts.pf the body and (c) the carotid arteries, which supply it to the brain. A human being contains about 70 ml of blood per Kilogram of body weight. For an adult, this is about 4 or 5 liters. The opening between various chambers of the heart are guarded by valves, which prevent the flow of blood in reverse direction. 4. Arterial system: A blood vessel, which carries blood away from heart to the various body parts is called an artery. The arterial system can be simply stated to comprise of the following three main components. Pulmocutaneous arteries: They supply deoxygenated blood to lungs and skin where it gives up carbon dioxide and picks up oxygen. Carotid arteries: These vessels arise from the truncus arteriosus, and supply the oxygenated blood to various parts of the head region such as brain, tongue, head muscles, eyes, ears etc. Systemic arteries: These vessels carry oxygenated blood to all the parts of the body except the head and lungs. They fuse together to form a major vessel of this system called aorta, which gives off branches to various parts of the body such as fore and hind limbs, digestive system, liver, pancreas, kidneys, genital organs and muscles. 5. Venous system: It is a set of blood vessel, called veins, which bring the blood from all the parts of the body towards heart. The venous system consists of the following major components.

(i) The oxygenated blood from the lungs is collected by pulmonary veins, which bring it to the left auricle of the heart.

(ii) The deoxygenated blood from head and fore limbs is collected through several veins, which join together to form one major precaval vein, on each side.

(iii) Blood from all the lower parts of the body such as stomach, intestine, liver, pancreas, genital organs, muscles, hind limbs etc, is collected through veins, which join together and form one major vein called post caval. Both the pre-cavals and the post-caval open into the sinus venosus from where the blood is pumped into the right auricle of the heart.



Portal system: Set of veins, which collect the blood from one organ and discharge it into another organ, is called portal veins. The set of veins draining their blood into liver are included in hepatic portal whereas the set opening into the kidneys are called renal portal system. Hepatic portal system: The veins collecting the blood from the digestive system do not carry it directly to the heart. They all join to form a hepatic portal vein, which breaks up into capillaries in the liver to allow transfer of some of the digested food into the liver for storage. From the liver, blood enters the post-caval, which carries it to the sinus venosus. Some of the blood from hind limbs is collected in an abdominal vein, which joins the hepatic portal vein in the liver and drains blood into liver from where it is collected by the post caval vein. These veins are also included hepatic portal system. Renal portal system: The alternate route of blood from the hind limbs is by the way of a renal portal vein. These veins begin in capillaries in the hind limbs and breaks up into capillaries in the kidneys. From the kidneys, this blood enters the post caval by renal veins and ultimately returns to the heart. These veins arc included in renal portal system. 6. Excretory system: It is the set of organs involved in the process of excretion i.e. the removal of metabolic waste matters from the body. This function is performed by kidneys, which filter out the excretory matter from the blood and pass it out in the form of urine. There are two kidneys in frog. They are elongated reddish brown organs attached to the dorsal wall of the body cavity. The urine is carried from the kidneys by a pair of tubes called ureters, which open into the cloaca. From the cloaca, it is either passed out directly through cloacal aperture or is stored for some time in a bag, the urinary bladder. 7. Reproductive system: Reproduction is the process of production of new babies by their parents. Organs involved in this process are included in reproductive system. Sexes are separate in the frog. The reproductive organs consist of gonads and their ducts. The gonads produce germ cells and the ducts pass them but of the body. The male gonad is known as the testis (plural testes) and the female gonad is called the ovary. The gonads are paired structures and are located near the kidneys. The sex cell of male is sperm and that of female is ovum (Plural ova) or egg. The ova are released into water through the cloaca in the mating season. The male produces sperms during the breeding season. Sperms are also released from the testes into water near the eggs. Each sperm fuses with a egg and a new frog starts developing. 8. Nervous system: The set of organs, which control and co-ordinate all the activities of the body is called nervous system. It is composed of two parts, i.e the central nervous system and the peripheral nervous system. The central nervous system includes the brain and the spinal cord whereas the peripheral nervous system comprises of nerves, which connect the central nervous system with various parts of the body, i.e. muscles, glands and sense organs.

The animal with the heaviest brain is the sperm whale. Its brain weighs about 9.2 Kg.

The brain is protected in the skull and the spinal cord is enclosed in the vertebral column. The brain consists of the following regions:

(i) The most anterior region comprises the olfactory lobes.



(ii) Immediately behind the olfactory lobes, there are two large outgrowths called the cerebral hemispheres.

(iii) Behind the hemispheres are located two prominent outgrowths called the optic lobes.

(iv) The part between the optic lobes and hemispheres is known as the diencephalon. On the dorsal surface of diencephalon is present a pineal body while the pituitary gland is attached to its ventral surface.

(v) The last part of the brain consists of the cerebellum and the medulla oblongata.

The spinal cord starts from the posterior end of the medulla oblongata like a thick thread. It passes from the skull through a hole and enters the canal of the vertebral column. The vertebral column protects the spinal cord just as the skull protects the brain. Brain and spinal cord are not solid. They have a system of canals which is filled with a fluid. Olfactory lobes are associated with the sense of smell and transfer of olfactory sensation to the cerebral hemispheres, which are the seats of intelligence and memory. The diencephalon receives a variety of messages from the internal and external environment of the body and also controls the secretion of hormones from the pituitary gland. The optic lobes are associated with the eyes and vision. The cerebellum and the medulla oblongata co-ordinate body movements and maintain balance of the body. The medulla also controls respiration, circulation and digestion. The spinal cord controls the movements of the trunk area, and many other functions independently. The peripheral system connects body parts with the central nervous system. This system consists of cranial and spinal nerves. Cranial nerves connect and establish communication between various parts of brain and parts of the head while the spinal nerves connect structures of the trunk area with the spinal cord. Some special nerves are present in the head and trunk region called the autonomic nerves, which work automatically. Autonomic nerves control the internal organs of the body such as heart, lungs, stomach, smooth muscles of the intestine, vessels and glands. 2.9 SENSE ORGANS To get the informations about the environment organisms like frog have receptor organs. These receptors send sensations to the central nervous system via nerves. The frog has many types of receptors. Its skin has many small microscopic receptors for the sense of touch. For smell, there are olfactory receptor located in the nostrils. For the sense of taste sensory cells are present in taste buds on the tongue. Ears are used for receiving sound waves and maintaining balancing and eyes for receiving light i.e. sight.

The animal with the most acute sense of smell is the male emperor moth. Using its antennae, it can detect a female emperor moth 11.Km upwind

The biggest mammalian tongue that has ever been weighed belonged to a Blue whale caught by Russian trawlers in 1947. Its tongue weighed 4.3 tonnes.

1. Ear: In frog, like the other vertebrates, the organ of hearing is the ear. Its outer most part is the tympanic membrane. An external ear called pinna is absent in frog. On the inner side of this membrane is a cavity known as tympanic cavity. The cavity contains three small rod- like bones called ossicles Its one end is attached to the tympanic membrane and the other with the internal ear.



High pitched sounds are rapid vibrations of the molecules In air. Human can hear sounds which vibrate at about 19 KHz. Some bats can hear ultrasonic sounds upto about 160 KHz. The internal ear (Fig: 2.43) is a very delicate organ. It consists of three semi-circular canals. These canals are filled with a fluid and sensory cells are located at special places in these canals. When sound waves strike the tympanic membrane it is set into vibration. This vibrates ossicles which in turn, vibrate the internal ear and thus, sound waves stimulate the hearing receptors in the inner ear. The internal ear, in addition to hearing, also keeps the balance of the body. 2. Eye: The frog has two eyes one on each side of the head (Fig: 2.44). If we make vertical section of the eye, we find that the innermost layer of the ball is the sensory retina. The retina contains photoreceptor cells. Outside the retina is the choroid, which is richly supplied with blood capillaries supplying nutrients to the retina. The sclerotic is the hard, outer most layer of the eye. It provides shape to the eye ball. The anterior transparent part of the eye is called cornea. Behind the cornea is iris. The iris has a window called the pupil. Behind the pupil is the lens of the eye. The cornea, pupil and lens focus light on the retina. A watery fluid is present in between the cornea and lens. Similarly a jelly like fluid is present between the lens and retina, through which light passes before it strikes retina. Optic nerve takes the sensory messages from the eye to the brain.



SUMMARY

Cell is the basic unit of living organisms. All the living organisms are made up of one or more cell. Cells are observed under light and electron microscopic. Resolution power of electron microscope is very much high. Plant cell consist of cell-wall, cell membrane, cytoplasm and nucleus, in an

animal cell all these parts are present except cell-wall. Prokaryotic cell is the type of cell with out proper nucleus while eukaryotic

cell contains proper membrane bound nucleus. Cell wall is non-living part of cell, mainly composed of cellulose and pectin. Cell membrane is a thin, differentially permeable membrane which limits the

cytoplasm. Translucent material filled in between nucleus and plasma membrane is called

cytoplasm. Cytoplasm contains many granular bodies called cytoplasmic organelles like,

endoplasmic reticulum, golgi bodies, lysosome, ribosome, mitochondria, plastids etc.

Cells divide to increase in numbers. Mitosis is the equational type of cell-division in which chromosome number

does not change. Meiosis is the reductional cell-division in which number of chromosomes

reduces to half. Tissues are the groups of similar cells. Amoeba is an example of unicellular organization, Brassica and frog of

multicellular organization EXERCISE 1. Fill in the blanks with appropriate terms:

i) Animals which consist of only one cell are called________ ii) Finger like projection in amoeba are called________ iii) Botanical name of mustard plant is__________ iv) Reproductive part of a higher plant is_______ v) Part of stem from where leaf arises is called

2. Write whether the following statements are true or false:

i) Gonads are the organs responsible to produce germ cells. ii) Brain and spinal cord are the parts of peripheral nervous system. iii) Pulmonary vein contains de-oxygenated blood. iv) Truncus arteriosus and sinus venosus are the true chambers of the heart of frog.

v) During pulmonary respiration gaseous exchange takes place through skin.

3. Encircle the appropriate answer:

i) Nucleus of cell was discovered by (a) Robert Hooke (b) Schleiden (c) Robert Brown (d) Virchow

ii) The type of lenses of light microscope is (a) Biconcave (b) Convex (c) Concave (d) Electromagnetic

iii) DNA is found in (a) Nucleus (b) Chromosome (c) Cell (d) Nucleoplasm

iv) Prokaryotic cells do not contain



(a) Nucleus (b) Membrane bound nucleus (c) Ribosome (d) Cell-membrane

v) The number of chambers in the heart of frog is (a) Two (b) Three (c) Four (d) Five

4. Write detailed answers of the following questions:

i) Make a chart of different types of plant tissues: ii) Draw a diagram showing different parts of a typical plant cell. iii) Describe those organelles which are only found in plant cell. iv) Describe digestive System of frog with the help of diagram. v) What is the difference between cellular respiration and gaseous exchange? Describe different methods of gaseous exchange in frog. vi) What do you mean by cell-division? Describe the method of cell-division by which gametes or spores are produced.

5. Give scientific reason of the following: i) Why is cell membrane differentially permeable? ii) Why is cell called the basic structural and functional unit of life?. iii) How do the chromosome number remains the same in the members of

same species? iv) Why is meiosis called reductional cell-division? v) Why is upper surface of dicot leaf much darker than the lower surface? 6. Define the following terms:

i) Cell ii) Tissue iii) Prokaryotic cell--------------- iv) Eukaryotic cell v) Chromosomes vi) Mitochondria------------------ vii) Connective tissue viii) Meiosis ix) Meristematic tissue---------- x) Compound tissue xi) Mitosis xii)Hibernation xiii) Neuron or Nerve cells

7. Distinguish between: i) Prokaryotic and eukaryotic cell. ii) Cell-wall and cell-membrane. iii) Mitochondria and plastids. iv) Light and electron microscope. v) Arteries and veins.

Class IX Biology Book Chapter 02

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Transcript of Class IX Biology Book Chapter 02