Biology 1 Unit 4: Chapter 5 (in book) – Cellular Respiration and Photosynthesis

I. Energy and Living Things

A. The ultimate source of energy for life on earth = SUN

B. Allows for photosynthesis

1. Light energy is converted to chemical energy and stored in organic compounds

2. Performed by autotrophs – they trap solar energy and convert it into food/chemical energy in the

bonds of glucose

C. Some autotrophs don’t carry out photosynthesis

1. They use chemical energy stored in inorganic substances to make organic compounds

2. These are prokaryotes that live in environments where there is no sunlight

a. Example: Bacteria near deep sea volcanic vents

3. Cellular respiration - metabolic process similar to burning fuel in an engine

a. Performed by heterotrophs because they can’t make their own food

b. Involves the mitochondria, oxygen, and food they eat to release stored energy in the bonds

from the food

i. Usually it is glucose (carbohydrates) that is broken down in the mitochondria

c. Heterotrophs rely on autotrophs to trap the energy from the sun for them; they get energy

from:

i. The food they eat (food chains/webs)

ii. They absorb it from the environment (like fungus)

D. Energy compounds

1. Glucose

a. In autotrophs it is a monosaccharide that is made during photosynthesis

b. In heterotrophs, glucose is broken down or burned in the mitochondria to make or recycle

more ATP (cellular fuel)

i. Aerobic – requires oxygen – more efficient because more ATP is recharged

ii. Anaerobic – without oxygen – less ATP is recharged

2. ATP – adenosine triphosphate – cellular fuel

a. It is a compound that stores energy in the bonds between the phosphate groups

b. Two major components

i. Adenosine = adenine (a nitrogen-base of DNA) and ribose sugar

ii. Three phosphate groups – the last phosphate gets broken off, releases energy that can be

used to do cellular work

c. Bonds are broken to do cellular work

d. Examples: contract a muscle, carry a nerve impulse, do active transport, hook amino acids

together to make proteins, move cilia and flagella

e. You always have a reservoir of ATP in your cells – you never run out

i. The last phosphate group can be added back on in order to recycle the ATP molecule

ii. The energy needed to reattach the last phosphate group comes from the food we eat

3. ADP - Adenosine diphosphate

a. What’s left after the third phosphate is removed from ATP

b. You have a reservoir of ADP and low energy phosphate groups waiting to be recycled and

hooked back together again.

c. You need energy to turn a low energy phosphate group to a high energy phosphate group

i. This has to happen before they will hook onto ADP to make ATP

ii. The energy needed to do this comes from the food we eat…breaking glucose, atom by

atom, in the mitochondria

4. ATP/ADP cycle:

a. ATP → ADP + P + energy (to do cell work)

b. ADP + P + energy (from glucose) → ATP

c. The energy from food recharges low energy phosphates so they can be hooked on

II. Photosynthesis: the process by which autotrophs trap energy from the sun to make glucose and oxygen

A. 6 CO2 + 6 H2O +energy → C6H12O6 + 6 O2 (Note: this is the reverse reaction of cellular respiration)

B. 3 Stages

1. Stage 1: energy is captured from sunlight

a. Known as “light reactions,” or “light dependent reactions”

b. Uses the spectrum of light

c. Pigment called chlorophyll in chloroplasts – absorbs energy and converts it to recharge ATP by a

series of reactions on the electron transport chain

d. Thylakoids – disk shaped structures inside the chloroplasts

i. Contains clusters of pigments - chlorophyll

ii. When light hits the pigments in the thylakoid disks, energy is transferred to the electron in

the chlorophyll pigment

iii. Energy transfer causes electron to jump to higher energy levels and eventually chlorophyll

loses these excited high energy electron

iv. The electron must be replaced, so the plants obtain water from roots

v. When the water is split (using enzymes from the thylakoid disks), chlorophyll “steals” the

electron from the hydrogen atoms of the water molecules

vi. The left over hydrogen ions (hydrogen) are used to recharge ATP later on

vii. The left over oxygen is the oxygen we breathe

viii. THE OXYGEN WE BREATHE COMES FROM THE SPLITTING OF WATER

2. Stage 2 – Conversion of light

a. The excited high energy electrons from chlorophyll are used to make/regenerate ATP

b. There’s a series of molecules in the thylakoid disks called the electron transport chain

c. Electron transport chain– they pass high energy electrons to recharge ATP

i. The first molecule receives the high energy electron and steals a little bit of energy before it

is passed to the next molecule

ii. The second molecule steals a little bit of energy before passing the electron to the 3rd

molecule

iii. By the time the electron gets to the end of the electron transport chain all the energy is

gone

iv. BUT this energy is used to convert low energy phosphate groups to higher energy so ATP

can be recharged

d. ADP + P + energy → ATP (this ATP is the energy source for the next set of photosynthetic

reactions)

3. Stage 3 – Storage of energy

a. Dark Reactions or Light Independent Reactions – Use ATP as energy source instead of the sun as

in stage 1 and 2

b. Carbon dioxide fixation - transfer of CO2 (that comes into the plant from the leaves) to organic

compounds like glucose

c. Calvin Cycle – series of enzyme assisted chemical reactions that produce a 3 carbon sugar

i. Steps in the cycle:

1. CO2 is added to a 5 carbon compound by the action of an enzyme to make a 6 carbon

compound

2. The 6 carbon compound splits into 2 parts of 3 C’s each

3. Phosphate groups from ATP and electrons are added to the 3 carbon compounds to

make 3 carbon sugars

4. One of the 3 carbon sugars is used to make organic compounds (including starch and

sucrose) which is stored for later use

5. The 2nd 3 carbon sugar is used to regenerate the initial 5 carbon compound (from 1st

step)

ii. Needs of Calvin Cycle = 3 carbon dioxides for each 3 carbon sugar. Therefore, A TOTAL OF 6

CARBON DIOXIDES ARE NEEDED TO MAKE ONE GLUCOSE

C. Factors that affect photosynthesis

1. Amount of light – increases with increasing light intensity

2. How much pigment is used – photosynthesis continues until all pigment is used up

3. Carbon Dioxide levels – photosynthesis continues as long as there is enough carbon dioxide for the

Calvin cycle and carbon dioxide fixation

4. Temperature Range – slows down with cooler temps

5. Amount of enzymes to help chemical reactions – needs a certain amount of enzymes for reactions

to continue

III. Cellular Respiration

A. Aerobic – requires oxygen

1. Metabolic reaction where glucose is burned with enough O2 – starts in cytoplasm finished in

mitochondria

2. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP

3. 1 glucose is broken down and can recharge a total of 36 ATP

4. Stages of Aerobic Cellular Respiration

a. Stage 1: Glycolysis – means to split sugar – glucose (6 carbon sugar) is split into two pyruvate (3

carbon each)

i. Occurs in cytoplasm

ii. Enzymes help split the glucose in half

iii. Glycolysis is same whether in muscle or yeast

1. Products: 2 net ATP and 2 pyruvate molecules

iv. Steps of glycolysis:

1. Glucose enters the cell (cytoplasm)

2. 2 ATP from reservoir is used to start reaction

3. When glucose splits it releases energy - this is just the right amount of energy to

recharge 4 ATP

4. Even though 4 ATP are recharged, the two that were borrowed have to be replaced

5. 4 hydrogens are produced and stored for a step at the end of respiration (NAD + H →

NADH)

b. Stage 2 - occurs in mitochondria

i. Krebs Cycle (aka citric acid cycle): there are many reactions that occur here, but the Krebs

Cycle is the stage where you need oxygen from the air you inhale and also where you give

off most of the carbon dioxide that you exhale

1. 2 pyruvate + 2 O2 → 2 6-carbon compounds + CO2

ii. Electron Transport Chain (electron transport chain)

1. Series of chemical compounds in mitochondria that pass electron down the chain

2. Occurs in and on folds inside mitochondria

3. Steps of electron transport chain

a. 24 electron are stripped away and enter the electron transport chain and the 24 p+

are set aside

b. Low energy electron and protons reunite to form hydrogen again

c. Hydrogen combines with oxygen molecules from the oxygen we inhale to form

water molecules

d. Key Idea: oxygen is needed to accept the newly reformed hydrogen's, so OXYGEN IS

KNOWN AS THE FINAL HYDROGEN ACCEPTOR

iii. Oxygen is needed in order to keep Krebs and electron transport chain going

iv. Without it the electron transport chain shuts down and this will eventually cause the Krebs

cycle to shut down

v. So the only stage that keeps going is glycolysis

5. Summary of Aerobic Cellular Respiration

a. Stage 1 - Glycolysis

i. Need 2 ATP from reservoir to get started

ii. Occurs in cytoplasm

iii. Need 1 glucose

iv. Produces net total of 2 ATP

v. Produces 2 pyruvate molecules (3 carbon compounds)

b. Stage 2A – Krebs Cycle

i. Need oxygen (from air we breathe)

ii. Produces most of CO2 we exhale

iii. A lot of hydrogen is given off and create a reservoir of hydrogens that are needed for the

electron transport chain

iv. 2 ATP are recharged

c. Stage 2B – electron transport chain

i. Needs 24 hydrogens from reservoir so it can get the 24 electron from the hydrogens

ii. 32 ATP are recharged

iii. Needs oxygen (inhale) to be the final acceptor of hydrogen in order to form water vapor

(which we exhale)

B. Anaerobic – does not require oxygen

1. Metabolic reaction where glucose is burned in a shortage of oxygen – occurs in cytoplasm

(fermentation)

2. Glucose is broken down and can recharge 2 ATP

3. Your body has a reservoir of ATP molecules in the cytoplasm at all times

4. Anaerobic respiration can produce different things depending on where it takes place

a. Animal Muscle: glucose → Lactic Acid + net 2 ATP (this makes muscles sore)

b. Yeast Cells: glucose → Ethyl Alcohol + Carbon Dioxide + net 2 ATP (this makes alcohol)

5. Key Idea: The electron transport chain needs oxygen to function

a. When oxygen levels are low, the electron transport chain shuts down because there’s not

enough oxygen to accept all of the hydrogens

b. If the electron transport chain shuts down the Krebs will shut down too

c. Result: Glycolysis is the only stage that can take place

6. Steps

a. 2 ATP are taken from ATP reservoir

b. The 3rd phosphate is broken off of each of the two ATP

c. The energy from breaking the phosphate is added to glucose

d. Glucose (6-C) splits into 2 pyruvates (3-C)

e. When glucose splits it releases enough energy to recharge 4 low energy phosphate groups to

high energy phosphate groups

f. 4 High energy phosphate groups hook up with 4 ADP to make 4 ATP

g. 2 ATP are net gained, 2 are paid back to the ATP reservoir

7. Once the pyruvates are formed your body (or a yeast cell) realizes that there isn’t enough oxygen

so Krebs and electron transport chain don’t happen, then one of the following will happen

a. Lactic Acid Fermentation

i. Vigorous exercise causes lactic acid fermentation because the body still splits glucose but

there is not any oxygen to make the electron transport chain work

ii. The hydrogens given off that are supposed to go to the electron transport chain are added

to the pyruvate to make lactic acid (HLAC)

iii. HLAC - irritates muscle fibers, makes you sore if it is not removed fast enough–

cardiovascular exercise (where you are forced to inhale a lot of oxygen) will help you get rid

of the HLAC and thus decrease soreness

iv. Products are: 2 net gain ATP and Lactic Acid (HLAC)

b. Alcoholic Fermentation

i. In yeast, 3-carbon pyruvate is broken down and converted into ethanol (ethyl alcohol) and

carbon dioxide is given off

ii. This occurs in yeast to make food and beverages

1. Wine and Beer

2. Carbon Dioxide causes bread to rise – each little hole in the bread was once a pocket of

CO2 – the temperature from baking breaks down the alcohol and drives off the CO2

8. Anaerobic Respiration Summary

a. In Muscles

i. Lack of sufficient oxygen

ii. Only stage is glycolysis

iii. Krebs and electron transport chain do not happen

iv. Need 2 ATP from reservoir to start

v. Products

1. 2 net ATP

2. Lactic Acid (HLAC)

b. In yeast cells

i. Lack of sufficient oxygen

ii. Only stage is glycolysis

iii. Krebs and electron transport chain do not happen

iv. Need 2 ATP from Reservoir to start

v. Products

1. 2 net ATP

2. 2 Ethyl Alcohol molecules

3. 2 Carbon Dioxide molecules

Biology I Unit 4: Chapter 6 (in book) – Chromosomes and Cell Division

I. Cell division (a.k.a. cell reproduction)

A. Reproduction types:

1. Asexual reproduction: reproduction that does not involve the union of gametes and in which a

single parent produces offspring that are genetically identical to the parent

a. Advantages – only need one individual (can conserve energy), no genetic change is good if

environment is stable, all individuals produce offspring, more efficient passing of genes

b. Disadvantages – no recombination of genes, genetically static, non-beneficial alleles stay in

population

2. Sexual reproduction: reproduction in which gametes from two parents unite

a. Advantages – offspring are genetically unique, favorable when the environment is not stable,

slower rate of reproduction but faster evolution within the population occurs (changes within a

species occur faster), lower extinction rates, fast removal of harmful mutations

b. Disadvantages – need two parents to expend energy, genetic recombination is

counter-productive if conditions are stable, only half of all individuals are producing offspring,

less efficient at passing on favorable, non-dominant genes, cost of recombination (a favorable

combination can be broken)

B. Unicellular Organisms (prokaryotic and eukaryotic) – the purpose of division in unicellular organisms is

for reproduction

1. Asexual reproduction in prokaryotic organisms is called binary fission

a. The cell doubles its DNA; one copy goes to one side of the cell and the other copy goes to the

other side; the cell then splits into 2 cells

b. Only one organism’s DNA is involved

c. Offspring are clones of the parent

2. Sexual reproduction in prokaryotes is called conjugation

a. Bacteria and protists exchange pieces of DNA under harsh, life threatening environmental

conditions

b. Steps:

i. Protein bridge forms between two organisms; they exchange DNA

ii. Cell then divides by binary fission

c. This is considered SEXUAL even though there is no egg and sperm, because there is exchange of

DNA

C. Multicellular organisms: purposes of cellular division:

1. To Grow: the DNA doubles and then the cell splits into 2; 2 then splits into 4; 4 splits into 8; etc.

a. Differentiation:

i. the process in which the structure and function of the cells of an organism change to enable

specialization of those cells leading to specific tissue types

ii. stem cells take on specific structures to perform specific functions

iii. the more specialized structures, the more specific the function of the cell

iv. stem cell becomes muscle (as opposed to a nerve cell, skin cell, etc.); muscle cell takes on

even more specialized structures to become a skeletal muscle cell or cardiac muscle cell or

smooth muscle cell

2. To Repair: In the damaged area, healthy, nearby cells undergo division/mitosis to fill in the

damaged area

II. Genes and chromosomes

A. Gene – segment of DNA that codes for the production of a protein that expresses a trait

B. Chromosomes – DNA and proteins associated with DNA

1. Can form strands which are a series of genes linked together

2. Chromosomes are DNA that have condensed into discrete units.

3. All species have a characteristic number of chromosomes. (humans = 46)

4. Doubled chromosome parts

a. Chromatids (sister chromatids) – 2 exact mirror image copies of DNA that make up a

“replicated,” or “double chromosome”; the original DNA and the DNA copy; physically and

genetically identical

b. Centromere – a structure that holds sister chromatids together (the dot)

C. Somatic Cell – any body cell other than an egg or sperm cell

D. Gametes – Sex cells: egg or sperm

III. The Cell Cycle

A. Organelles and locations

1. Spindles – cell structures made of centrioles and microtubules (spindle fibers) that hold and guide

the chromosomes during cell division

2. Centriole – structures at the opposite poles (“sides”) of the cell; they hold the ends of the spindle

fibers in place

3. Equator – the center of the cell when the nucleus is gone

B. The cell cycle

1. A repeating sequence of cellular growth and division

2. Involves a series of steps

3. Interphase – the cell spends 90% of its time in this phase; not a step in mitosis, but prepares cell

for mitosis

4. Mitosis – division of the nucleus

5. Cytokinesis – division of the cytoplasm and organelles; not a step in mitosis, but begins during

mitosis

IV. Mitosis

A. When the nucleus of a cell divides into two identical portions resulting in 2 identical daughter cells

B. “MITOSIS” is subdivided into 4 phases:

1. Prophase

a. Chromosomes shorten and thicken until they are visible

b. Nuclear membrane begins to break down

c. Spindle begins to form by having centrioles move apart while the microtubules stretch across

between the centrioles

d. Each doubled chromosome hooks on to its personal spindle fiber, and each begins to move to

the equator along its personal microtubule

2. Metaphase – “meta” means “middle”

a. Doubled chromosomes meet in the middle along the equator of the cell

b. Each sister chromatid faces her own pole (or side of the cell)

3. Anaphase - “ana” means “back”

a. Centromeres split

b. Single stranded, daughter chromosomes begin to be pulled to opposite sides of the cell as

spindle fibers break

c. “ana-banana split”

4. Telophase – “telo” means “end”

a. Single stranded chromosomes arrive at opposite sides of the cell

b. Nuclear membrane re-forms

c. Spindle and spindle fibers break down

d. Chromosomes uncoil and go back to chromatin granules

C. Result of Mitosis

1. Mitosis produces BODY CELLS not sex cells

2. Daughter cells (2n) are identical clones to the original parent cell (2n)

3. Allows the multicellular organism to grow and replace damaged tissue

4. You start with one cell and end up with 2 smaller cells

V. Cytokinesis - division of the cytoplasm

A. Cytoplasm and organelles divide in ½ along the equator so each daughter cell has equal nucleus,

cytoplasm, and cell organelles

B. Animal cells – a cell furrow forms- an indentation forms along the place where the equator is located

C. Plant cells – doesn’t form a cell furrow but instead forms a cell plate, which is a new piece of cell wall

that begins to form at the equator and grows outward