Multicellular Organisms

Key Area 2.1: Producing New Cells

Producing New Cells

Learning Intentions

• Describe the stages of mitosis

– Understand the terms chromatids, equator and spindle fibres

• Explain why cells undergo mitosis

– In terms of growth and repair

– In terms of maintaining chromosome compliment

• State that stem cells are unspecialised

– Explain what is meant by the term “cell specialisation”

• Describe the levels of organisation found in animals

Everyone in this room started life as a single cell, a fusion of a sperm

and egg cell.

What processes must have happened to develop you from that single cell?

How many new cells do you think you will make in a day?

Cell Division throughout Life

330 000 000 in 20 minutes so…

23,760,000,000 new cells every day!

What do these pictures all have in common?

They are all examples of cell division in action for growth or

repair!

How do Cells Divide?

Mitosis – watch this clip on the process of mitosis and answer the following questions:

1.How are new cells produced?

2.What are chromosomes? Where are they found?

3.What kind of cells undergo mitosis?

4.What are the only kind of cells that do not undergo mitosis?

Mitosis

• Mitosis is the process by which the nucleus divides into two daughter nuclei, each of which receives exactly the same number of chromosomes as were present in the original nucleus.

• As each chromosome becomes shorter and thicker, it is seen to be a double thread. Each thread is called a chromatid.

• The two chromatids of a chromosome are joined together by a centromere.

• The membrane of the nucleus disappears and spindle fibres form.

Mitosis

• A spindle fibre attaches to each centromere as the chromosomes line up along the ‘equator’ of the cell.

• Next, each centromere splits and one chromatid from each pair moves to opposite ends (or poles) of the cell.

• Finally, a new membrane forms around each nucleus and mitosis is complete.

• Mitosis is followed by division of the cytoplasm to form two identical daughter cells.

• Mitosis ensures the continuity of the diploid chromosome compliment from during cell division.

Diagram taken

from National 5

Biology by J.

Torrance

Diagram taken

from National 5

Biology by J.

Torrance

Chromosome Complement

• The number of chromosomes that a species of animal or plant possesses.

• Why do you think it is important that each new cell has the same chromosome complement as the parent cell?

• During growth and development of an organism, the chromosome compliment will be able to provide the animal or plant with all the characteristics of its species.

• Losing any chromosome would mean a loss of genetic information – the information that forms the code allowing the cell to function correctly!

Chromosome Complement

Stem cells

Stem cells are found in animals. They are unspecialised cells which can divide by mitosis to develop into specialised cells.

Stem cells are found in early embryos –embryonic stem cells – and in adults –tissue stem cells.

Embryonic stem cellsFound only in early embryos.

Can develop into any type of cell.

Allow us to growfrom tiny embryo to a fully formed baby.

Found throughout the body in adults and children.

Use mainly for repair. They cannot form as many specialised cells.

Tissue stem cells

Medical uses of stem cellsSource of stem

cellMedical use

Use page 79+80 to complete this table

Stem cell controversy

Carry out some research into the issues surrounding stem cell research (scibrbrain)

Write a short essay:

Introduction – introduce the issue.

Arguments for – give 2 or 3 arguments in favour of using stem cells from embryos.

Arguments against – give 2 or 3 arguments against using stem cells from embryos.

Conclusion – what is your opinion?

Specialisation in animal cells

Cells in plants and animals show specialisation. This means they have a special shape or structure that allows them to carry out a specific function.

Cells

Tissues

Organs

Organism

Levels of organisation in animals

What do all these have in common?

WHAT IS A SPECIALISED CELL?

Plants and animals consist of many cells andso are known as multicellular

They contain many different types of cells.

Each type of cell is designed to carry out aparticular job or function.

Not all cells look the same.

Some cells have a special shape and featuresto help them do a certain job.

SPERM CELL

.

Sperm Cell

• A sperm cell’s function is it’s involved in fertilisation.

• A sperm cell has a tail so it can swim towards the egg cell.

Red Blood Cell

• A red blood cells function is to carry oxygen.

• A red blood cell has a large surface area and no nucleus so it can carry more oxygen.

National 5 Textbooks

• Page 77 Q1-3

• Page 82 Q1.

Key Area 2.2: Control and Communication

a. Nervous System

b. Hormonal System

Nervous System

Learning Intentions

• List parts of the nervous system.– CNS and other nerves.

• Give details of the functions of the different structures of the brain.– Cerebrum, cerebellum and medulla

• State the 3 types of neurone– Sensory, inter and motor

• Describe how an impulse is generated and transmitted.

Twig videos

Neurons as cells

Neurons as networks

The Brain

Part of the brain Function

Cerebrum Enables conscious thought and memory

Cerebellum Controls co-ordination and balance

Medulla Controls breathing and heart rate

Nervous systemThe nervous system

is comprised of:1. Peripheral

nervous system2. Central nervous

system (CNS).The CNS is made of

the brain and the spinal cord.

Gathering informationThe sense organs -

collect information from the environment.

Receptor cells are present in the sense organs which detect stimuli (changes in conditions).

This information is transmitted to the CNS through sensory neurons.

Responding to information

The CNS processes the information and decides on what response to make.

The responses travel along a motor neuron to effectors e.g. muscles or glands.

Senses

Sensory Neuron

CNS

Motor neuron

Effector

Response

Stimuli

Effectors

Different effectors bring about different responses.

e.g. A muscle will bring about a fast response.

A gland will bring about a slower response.

Reflex arc

Reflex actions do not require conscious thought.

If you touch something painful, the receptors in the skin send an electrical impulse along the sensory neuron to a inter neuron. This passes the signal to a motor neuron and onto the effector.

Senses

Sensory Neuron

INTER NEURON

Motor neuron

Effector

Response

StimuliBy not involving the conscious brain the reflex is quick and prevents a greater injury from occurring.

Synapses Neurons do not directly touch each other.

Between two neurons there is a tiny gap called a synapse.

Signals move from one neuron to another by chemicals called neurotransmitters.

Hormones

Learning Intentions

• State the origin, transport and target of hormones.

• Describe the role of hormones in blood glucose regulation.– Insulin and glucagon.

– Glycogen, pancreas and liver.

Hormones

Hormones twig video

Multicellular organisms using chemical messengers, called hormones, to send messages from one part of the body to another.

Hormones are produced by endocrine glands, all round the body, and travel in the blood to their target tissue.

Hormones are specific to their target tissue.

Target tissues have special receptors in their cell membrane which will recognise specific hormones.

So a hormone will only work on their target tissue (similar to enzymes).

Endocrine glandsTask: Using the

internet, find examples of a hormone produced by each of these glands.

Complete this table:Gland Hormone Target

tissueRole in the body

Hormones in action: Blood glucose levels

Glucose is essential in animals as a source of energy. Cells in the body require a constant supply of glucose for respiration to occur.

Glucose is transported around the body in the blood and its levels must be tightly controlled.

After a meal1. After eating blood sugar levels

increase. 2. This is detected by cells in the

pancreas.3. The pancreas releases a hormone

called insulin into the blood.4. The insulin then travels to the liver.5. This activates enzymes in the liver

which convert glucose into glycogen.

5. The glycogen acts as a carbohydrate store and this brings the blood glucose levels down to the normal set point.

In between meals

1. In between meals blood glucose levels decrease as it is used up for respiration.

2. This is detected by cells in the pancreas.

3. The pancreas releases a hormone called glucagon. (= “glucose gone”)

4. The glucagon travels to the liver.

5. It activates enzymes in the liver which convert the glycogen back to glucose.

6. This raises the blood glucose levels to their normal set point.

In summary…

Diabetes

Nearly a ¼ million people in Scotland suffer from diabetes.

This is a condition that affects the body’s ability to control blood glucose levels.

There are two types of this condition:

Type 1 and Type 2

Type 1 and Type 2 diabetes

Type 1 diabetes

Type 2 diabetes

Cause

Treatment

Use in the information on page 140 to complete this table.

Importance of controlling blood glucose

High blood glucose levels, caused by type 1 and type 2 diabetes, can cause damage to blood vessels – especially those in the eyes and kidney. This can lead to damaged vision and kidney failure.

Polyuria (frequent urination), and blurry vision are also symptoms of undiagnosed diabetes.

Key Area 3: Reproduction

a. Diploid vs. Haploid

b. Gamete Production

c. Fertilisation

Diploid vs. Haploid

Learning Intentions

• Explain the chromosome complement of somatic cells.

• Explain the chromosome complement of gametes.

Sexual reproduction

Sexual reproduction involves combining the genetic information of two individuals.

The offspring produced by sexual reproduction are similar to their parents by not identical.

Chromosome complement

The number of chromosomes in a cell is called the

chromosome complement.

In humans this is 46 chromosomes.

Organism Number of chromosomes

Dog 38

Human 46

Donkey 62

Elephant 56

Rabbit 44

Snail 24

Cabbage 18

Gamete Production

Learning Intentions• State the names of the gametes produced by

animals.

• State the sites of gamete production in animals.

• Describe the structure of sperm and eggs.

• State the names of the gametes produced by plants.

• State the sites of gamete production in plants.

Gametes

• Sex cells are known as gametes.

• The gametes in animals are the spermand the egg

Cell

membranecytoplasm

nucleus

Tail

Where are sperm made?

Sperm are made in the

testes

Where are eggs made?

Eggs are made in the

ovary

• Collect the diagrams of the male and female reproductive organs.

• Highlight the parts where gamete production takes place.

Fertilisation

Learning Intentions

• Describe the process of fertilisation in animals.– Zygote and embryo formation.

• Describe the process of fertilisation in plants.– Pollination, zygote, embryo and fruit

formation.

Fertilisation

Fertilisation is the fusion of the male gamete nucleus with the female gamete nucleus forming a zygote.

Sexual reproduction summary video

Internal v. External fertilisation

In order for fertilisation to occur the sperm require a liquid environment.

In many aquatic animals e.g. fish, frogs, fertilisation occurs outside the body. The offspring then develop outside the body.

In humans, and other land animals, fertilisation occurs inside the body.

Gametes in plants

In plants the male gamete is pollen and the female gamete is the ovule.

The reproductive organs of plants are located in the flower.

Pollen is produced by the anther.

The ovule is produced by the ovary.

Label the diagram of the flower

Pollination

Pollination is the transfer of pollen from the anther of one plant to the stamen of the other.

Pollination can be caused by the wind or by insects.

Insect pollinated plants have flowers to attract insects.

While wind pollinated plants have anthers and stigma that hand outside the plant to catch the wind.

Fertilisation

In order for fertilisation to take place, the pollen must reach the ovule nucleus.

To do this the pollen grows a pollen tube:

The pollen lands on the stigma.

It begins to grow a pollen tube towards the ovary.

The haploid pollen nucleus then fuses with the haploid ovule nucleus to form a diploid zygote.

Haploid

Pollen

nucleus

Haploid

Ovule

nucleus

Key Area 4: Variation and Inheritance

a. Discrete Variation vs. Continuous Variation

b. Genetic Vocabulary

c. Monohybrid Crosses

d. Phenotype Ratios

Discrete Variation vs. Continuous Variation

Learning Intentions

• State the type of inheritance that causes discrete variation and continuous variation.

• Identify examples of discrete variation and continuous variation.

Variation

Sexual reproduction creates an organism that is different from all the other members of its species. This means sexual reproduction contributes to variation within a species.

There are two types

Discrete

Continuous

Discrete variation

Is where a characteristic fall into distinct groups, examples are

Blood group

Tongue rolling

Attached ear lobes

Investigation

We will carry out a survey in the class to find out how many people can roll their tongue.

Copy and complete the table belowCan roll tongue Cannot roll tongue

Number of pupils

Draw a bar chart to display your results!

Continuous variation

Is where a characteristic can have any value in a range examples are:

Height

Weight

Genetic Vocabulary

– Gene

– Allele

– Phenotype

– Genotype

– Dominant

– Recessive

– Homozygous

– Heterozygous

– P generation

– F1 generation

– F2 generation

Learning Intentions

• Define the following genetic terms:

What is a gene?

A gene is a single piece of genetic information made from DNA. It carries the information to create a particular characteristic. Genes exist in different forms called Alleles, which give different versions of the same characteristic.

• PHENOTYPE is the physical appearance resulting from the inherited information

• Example - Someone with blue eyes has the phenotype blue eyes.

• Genes or alleles can be said to be DOMINANT (shows up in the phenotype) or RECESSIVE (hidden when it is present along with the dominant gene).

• GENOTYPE is the combination of genes in a gene pair.

• Genotype is represented by 2 letters (one letter for each gene)

Dominant brown gene

So what is the Phenotype?????

Homozygous or Heterozygous

• Let B represent black coat colour in mice• Let b represent white coat colour

• BB has the phenotype black it is said to have a HOMOZYGOUS genotype (this is often called ‘pure breed’)

• Bb has the phenotype black but is said to have a HETEROZYGOUS genotype

• bb has the phenotype white and is said to be HOMOZYGOUS recessive.

Monohybrid Crosses

Learning Intentions

• Explain and perform monohybrid crosses from P to F1 to F2 generations

Gregor Mendal

A cross between two true-breeding parents that possess different forms (alleles) of one paricular gene is called a monohybrid cross.

Gregor Mendal an Austrian monk performed early monohybrid crosses using varieties of pea plant which possessed characteristics showing discontinuous variation.

Carrying out a monohybrid cross

The parental generation is P1The first generation is F1 The second generation is F2Problem……A true breeding black mouse mates with a white mouse and all the offspring are black. Two of this generation then mate.

- State which allele is dominant and which allele is recessive - Give genotype and phenotype of the parent mice - Give genotype and phenotype of F1 and F2 generations- Give ratios of black coat to white coat in F2.

Polygenic Inheritance

Most characteristics shown by plants and animals are polygenic, this means they are controlled by many genes that act together. Polygenic characteristics show continuous variation.

Genotype & Phenotype Ratios

• Often, the ratios of genotypes and phenotypes of the offspring do not exactly match those predicted by calculations.

• This is because genetic inheritance is random.

Phenotype Ratios

Learning Intentions

• Calculate the ratio of phenotypes resulting from a monohybrid cross

Key Area 5: Transport Systems – Plants

a. Plant Organs

b. Water Transport

c. Transpiration

d. Sugar Transport

Plant Organs

Learning Intentions

• Recall the organs of plants.– Roots, stems and leaves.

• Identify and explain the function of leaf structures.– Upper epidermis, palisade mesophyll, spongy

mesophyll, vein, lower epidermis, guard cells and stomata.

Plant Organs

Plants have 3 basic organs:- Roots (to anchor the plant

and absorb water and minerals).

- Stems (to support the leaves and transport materials through the plant)

- Leaves (for photosynthesis, gas exchange and transpiration.

The leafCollect a copy of this diagram.

The leafCollect a copy of this diagram.

Vein

Mesophyll Cells

• Palisade mesophyll cells are closely packed together to allow for maximum light absorption.

• Spongy mesophyll cells have air spaces between them to allow for easy gas exchange.

Importance of transport systemsPlants need transport systems to supply

the raw materials for photosynthesis and to remove the products.

Carbon dioxide

Water Glucose OxygenLight

Chlorophyll

Diffuse through stomata

Xylem Phloem

Water Transport

Learning Intentions

• Describe how water and minerals enter and are transported through plants.– Root hairs.

– Xylem vessels.

Xylem

The role of the xylem is to transport water from the roots to all other areas of the plant.

The xylem plays an important role in the transport of minerals which are dissolved in the water.

It also helps strengthen the stem of the plant.

National 4/5 Biology Course Unit 2

The xylem is a hollow tube of dead cells.

The xylem is strengthened by rings of lignin.

Water moves in an upwards direction from the roots.

Stomata

Use nail varnish and sellotape to remove look at stomata on the bottom of a leaf.

Your teacher will show you how. Draw what you can see under the microscope.

Stomata are pores on the surface of leaves.

Stomata allow carbon dioxide and oxygen to enter/exit the leaf.

They also allow water vapour to leave the leaf by evaporation.

Stomata made from two guard cells. Water is pumped into or out of the cells to open or close them.

Dark

Little water supply

Closing helps prevent water loss.

Light

Good water supply

Transpiration

Learning Intentions

• Describe the process of transpiration.

• Explain how certain factors affect the rate of transpiration.– Wind speed, humidity, temperature and

surface area.

TranspirationWatch this clip http://youtu.be/w6f2BiFiXiM

Water travels up from the roots in the xylem to the leaves. In the leaves it moves by osmosis from cell to cell and then evaporates into the gaps in the spongy mesophyll cells.

If the stomata are open the water vapour will diffuse out of the leaf. This is called transpiration.

National 4/5 Biology Course Unit 2

roots

stem

Water enters roots by osmosis

Water and ions pass up xylem

The movement of water through the plant is called the transpiration stream

Transpiration -water evaporates from leaves

Mineral ions enter by active transport

Photosynthesis produces sugar in the leaves

Sugar is transported in phloem

TranspirationWind speed: Increasing wind speed increases transpiration, and vice versa.

Humidity: Increasing humidity decreases transpiration, and vice versa.

Temperature: Increasing temperature increases transpiration, and vice versa.

Surface area: Increasing surface area increases transpiration, and vice versa.

Sugar Transport

Learning Intentions

• Describe how sugar istransportedthrough plants.– Phloem tissue.

PhloemAs well as transporting water and

minerals, plants have to transport the sugar from photosynthesis from the leaves to other parts of the plant.

This is carried out by special cells called phloem.

The phloem are living cells.

Phloem cells are connected by sieve plates.

Have a companion cell.

2.6: TRANSPORT SYSTEMS -ANIMALS

Learning Intentions

• State that the blood contains:– Plasma.

– Red Blood Cells (RBC’s).

– White Blood Cells (WBC’s).

• Describe the structure of a Red Blood Cell and its function.

• Give the 2 types of White Blood Cell’s, and their functions.

Why do we need blood?

• Blood allows substances to be transported from one place to another

• The human body takes in essential substances that need to be transported to other parts of the body.

• It also produces waste, which must be removed.

What is blood made up of?

• Red Blood Cells (RBC’s)

• White Blood Cells (WBC’s)

• Plasma.

THE BLOODBlood is made up of 2 main parts

SOLID PARTLIQUID PART

Red blood cells - carry 02 as

oxyhaemoglobin

White blood cells– destroy disease causing microbes

Plasma

-contains substances such as Glucose & CO2

Red Blood Cells• Involved in the transport of

Oxygen around the body.

• Contain a protein called Haemoglobin.

• Picks up oxygen in the lungs.

• Becomes a substance called OXYhaemoglobin.

• RBC’s do NOT have a nucleus or a mitochondria.

• This allows them to transport oxygen around the body efficiently.

Red Blood Cells – disc shape cells which contains the

protein haemoglobin that carries oxygen to body cells.

White Blood Cells

• White blood cells are part of the immune system and are involved in destroying pathogens.

• There are two main types of cells involved. Phagocytes carry out phagocytosis by engulfing pathogens.

• Some lymphocytes produce antibodies which destroy pathogens.

• Each antibody is specific to a particularpathogen.

What are pathogens?

• Pathogens are disease causing micro-organisms.

• There are 3 types:– Bacteria

– Virus

– Fungi

Phagocytosis

• In this process, a phagocyte engulfs a pathogen.

• The pathogen is then destroyed by digestive enzymes.

Production of Antibodies

• Lymphocytes produce antibodies, which destroy pathogens.

• Each antibody is specific to a particular pathogen.

The Heart

Learning Intentions

• Describe the pathway of blood through the heart, lungs and body.

• Describe the parts of the heart including:– Left Atrium

– Right Atrium

– Right Ventricle

– Left Ventricle,

– Location of the blood vessels & the valves.

Structure of the Heart• The heart has 4

chambers.

• The 2 upper chambers are called the Atria.

• The 2 lower chambers are called the Ventricles.

• The heart pumps blood to the lung where it picks up oxygen.

The blood vessels of the heart• VENA CAVA – Veins that carry

deoxygenated blood from the body to the right atrium.

• PULMONARY ARTERIES – Arteries that carry deoxygenated blood from the right ventricles to the lungs.

• PULMONARY VEINS - Veins that carry oxygenated blood from the lungs to the left atrium.

• AORTA – An artery that carries oxygenated blood from the left ventricle to the rest of the body.

Pulmonary artery

Pulmonary vein

Vena cava

Aorta

Blood vessels in the heart

Label these

vessels on your

diagram

valves

valvevalve

The valves in the heart

Label these

vessels on your

diagram

The Pathway of Blood• The next slide shows the flow of blood

through the heart to the lungs and the body:

BodyVena

Cava

LungsAorta

Pulmonary

Artery

Right

Atrium

Left

Ventricle

Left

Atrium

The red blood is oxygenated

The blue blood is deoxygenated

Where there is a combination – diffusion is taking place

Right

Ventricle

Pulmonary

Vein

Circulatory SystemPulmonary artery

Pulmonary vein

Aorta

Hepatic artery

Mesenteric artery

Hepatic vein

Hepatic portal vein

Renal arteryRenal vein

Vena cava

The Coronary Arteries

• The heart receives it’s blood from the CORONARY ARTERIES.

• These are branches off the AORTA.

• The coronary arteries ensure that the heart muscle receive a good supply of glucose and oxygen to carry out respiration & release energy.

The Coronary Arteries of the Heart

Teacher Demo: Heart Dissection

Learning Intention

• Describe the structure of:– Arteries.

– Veins

– Capillaries.

Blood vessels

There are three types of blood vessels.

blood from the heart

blood to the heart

Capillaries carry blood to and from the body’s cells

Veins carry blood back

into the heart

Arteries

carry blood

away from

the heart

Blood vessels

Arteries:

Carry blood away from the heart.

Have a thick muscular wall. narrow central channel

(lumen). carry blood under high

pressure. When the heart pumps

blood into an artery, it can be felt as a pulse.

Elastic Wall

Ring of Muscle Blood

Blood vesselsVeins:

Return blood to the heart.

Have thin walls. wide central channel

(lumen). carry blood under low

pressure. contain valves which

prevent the backflow of blood. Thin

Inelastic Wall

Blood

vein valve open

Blood vessels: valves

blood to the heart

backflow prevented

vein valve closed

The valves allow blood to

flow in the correct direction…

…but close if blood starts to

flow in the wrong direction.

Function: To prevent the backflow of blood.

Blood vessels

Capillaries:

Form networks at organs and tissues.

Thin walled - only one cell thick.

Allows exchange of materials.

Large surface area to allow quick, efficient rate of diffusion.

Very thin wall

Blood

2.7 Absorption of Materials

Learning Intentions• Explain & describe why oxygen and

nutrients are required by cells.

• Explain & describe why waste materials such as CO2 have to be removed from cells.

• State why tissues contain capillary networks.

• Describe how absorption of materials occurs and the features that allow it to happen efficiently.

Why does absorption take place?

• Oxygen and nutrients from food must be absorbed into the bloodstream to be delivered to cells for respiration.

• Waste materials, such as carbon dioxide, must be removed from cells into the bloodstream, and then excreted out of the body.

• One way of doing this is in the tissues.

• Tissues contain capillary networks to allow the exchange of materials at cellular level.

Absorption of materials (2)• Surfaces involved in the absorption of

materials have certain features in common: – Large surface area.

– Thin walls.

– Extensive blood supply.

• These increase the efficiency of absorption.

• Examples where absorption takes place are the lungs, and the villi of the small intestine.

The Lungs

Learning Intentions

• State that the lungs are the organs of gas exchange.

• Describe the structure of the alveoli.

• Describe how gas exchange occurs in the lungs.

The Breathing System

• We breathe air in through our nose & mouth.

• It then passes through the trachea towards the lungs.

• The larger airways (such as the trachea) are held open by rings of cartilage.

• Air travels through the Bronchi, and then the bronchioles.

• At the end of the bronchioles are air sacs called alveoli.

Windpipe / Trachea

Intercostal Muscle

Bronchioles

BronchiDiaphragm

Air Sac

Rib

Ring of Cartilage

Lung

The lungs are the organs designed for gas exchange

Rings of cartilage Stop windpipe closing

Trachea / Windpipe Carries air towards the lungs

Bronchioles Tiny tubes which run to air sacs

Air sacs Where O2 and CO2 are

exchanged with the blood

Blood capillaries Tiny blood vessels that exchange

gases with air sacs

Diaphragm Large muscle that forces air

Into and out of lungs

Intercostal muscles Muscles between ribs that move

chest up and out on contraction

Bronchi Branches of the windpipe

that carry air to each lung

Structure of lung Function

• The trachea and bronchi are held permanently open by incomplete rings of cartilage.

• The rings of cartilage ensure that the airway is kept open.

Cartilage

Absorption in the lungs -Alveoli

• The alveoli are the site of gas exchange in the lungs.

• They allow Oxygen & Carbon Dioxide to diffuse into & out of the blood.

• It is important that gas exchange happens quickly & efficiently.

• The following information shows the ways that the alveoli are adapted for efficient gas exchange:

1. There are millions of alveoli in the lungs, increasing the surface area for diffusion to take place.

2. The alveoli are surrounded by a dense network of capillaries, giving them a good blood supply.

3. The walls of the alveoli are one cell thick, meaning diffusion must take place over a very short distance.

4. The lining of the alveoli is moist to allow gases to dissolve before they diffuse.

Feature Provided by Advantage

large surface area many alveolilarge volumes of

gases can be exchanged

blood has continual O2 uptake and CO2

removal

large capillary network

good blood supply

reduces distance which gases have to

diffuse

single celled wall of alveolus and

capillary

very thin walls

moist surfaces fluid lining the alveolus

O2 must dissolve before it can diffuse

through cells

Bronchiole

Capillary

Alveolus

Diffusion at the alveoli

The Digestive System

Learning Intentions

• Describe how nutrients are absorbed into the villi of the small intestine.

• Know the structure of the villi.

Mouth

Tongue

Gullet or Oesophagus

StomachLiver

Gall Bladder

Bile Duct

Pancreas

Small Intestine

Large Intestine

Appendix

Rectum

Anus

The alimentary

canal (the gut) is

long muscular tube

running from the

mouth to the anus.

Absorption in the Small Intestine

• Nutrients from food are absorbed into the villi in the small intestine.

• The large number of thin walled villi provides a large surface area.

• Each villus contains a network of capillaries to absorb glucose and amino acids and a lacteal to absorb fatty acids and glycerol.

The Small Intestine

• The small intestine is made up of structures called villi.

• Villi are responsible for absorbing the products of digestion.

To absorb food efficiently the small intestine has three main adaptations.

1. It has a very large surface area. This is because:

(a) It is very long (6 meters from end to end).

(b) The inner surface is folded and covered with many finger-like projections called Villi.

Wall of

the Villi

2. The walls of the small intestine are very thin e.g. one cell thick. This allows rapid absorption of materials.

3. The small intestine has a very good blood supply. This allows the products of digestion to be carried away quickly.

Blood

Capillary for

absorption

of glucose

and amino

acids.

Lacteal

Each villi has a central lacteal.

This is to carry away the products of fat digestion.

Thin wall of villi

Capillary (glucose and

amino acid absorption)

Lacteal (fat absorption)

Collect and label a

villi diagram.