Life Sciences

Condensed material

Life Sciences

Photosynthesis:

What is photosynthesis?

It’s the chemical process by which carbohydrates (glucose) is produced, using radiant energy.

Word Equation – raw materials: carbon dioxide + water + radiant energy in the presence of chlorophyll and enzymes = products: glucose and oxygen

There are two phases pf photosynthesis, a light dependent and a light independent phase. The light dependent phase requires light to complete its function and the light independent phase can complete its function in the presence or the absence of light.

A) The light dependent phase – takes place within the grana of the chloroplast

1.

The required radiant energy is absorbed by the chlorophyll in the grana

2.

Water is absorbed into the grana of the chloroplast

3.

The radiant energy causes the water molecule to split (photolysis), releasing:

4.

Hydrogen ions, which are taken into the light independent phase and

5.

Oxygen which is released back into the atmosphere

6.

Radiant energy also causes ATP to be formed (phosphorylation) which is taken into the light independent phase

B) The light independent phase – takes place within the stroma (cytoplasm) of the chloroplast

1. Carbon dioxide is absorbed from the atmosphere

2. Carbon dioxide and hydrogen ions, from the light dependent phase are combined using ATP, to form carbohydrates (glucose)

3. Excess glucose is stored as starch in starch granules

Factors that can influence photosynthesis:

The intensity of light:

1.

At low intensity, the rate of photosynthesis is low

2.

As the light intensity increases, the rate of photosynthesis also increases (directly proportional) this will happen up to a certain point

3.

When light intensity is at the optimum amount, photosynthesis will occur most rapidly

4.

If the light intensity increases past the optimum, the rate of photosynthesis will remain constant, the other factors such as carbon dioxide become limiting factors which reduce the rate of photosynthesis

The concentration of carbon dioxide:

1.

At a low carbon dioxide level, the rate of photosynthesis is low

2.

As the carbon dioxide level increases, the rate of photosynthesis also increases, this will happen to a certain point.

3.

When the optimum amount of carbon dioxide is present, photosynthesis will occur most rapidly.

4.

If the carbon dioxide concentration is higher than the optimum amount, then photosynthesis will remain constant.

How high temperatures affect the rate of photosynthesis:

1.

When temperature is low, the rate of photosynthesis is low

2.

As the temp increases, the rate of photosynthesis also increases

3.

When temperature is at the optimum amount, the rate of photosynthesis will reach a maximum.

4.

If the temperature is higher than the optimum amount, the rate of photosynthesis will decrease, since the enzymes used in the process of photosynthesis will denature at high temperatures and will no longer function.

Cellular respiration: inside the cytoplasm and mitochondria of cells

Reactants of cellular respiration – glucose + oxygen

Products of cellular respiration – carbon dioxide + water + ATP

Aerobic respiration: respiration in the presence of oxygen

Anaerobic respiration: respiration in the absence of oxygen

Investigation: Oxygen is used during cellular respiration:

Aim: to show that oxygen is used during cellular respiration

Method –

1.

Use germinating beans – they are living and actively respiring, therefor they make use of oxygen to release energy during cellular respiration

2.

Ensure that the equipment is sterilized – (so that no microorganisms can influence the results)

3.

Place some of the beans in boiling water – (this kills the beans and ensures that no cellular respiration can take place in them)

4.

Setting up the apparatus, make sure that the test tubes are tightly sealed – (this ensures that no outside air can enter or escape ensuring that any change in carbon dioxide or oxygen is due to the respiration of the beans)

5.

Leave the test tubes overnight – (to provide the germinating beans enough time to respire, so that enough oxygen can be used and carbon dioxide can be produced to measure results)

6.

Take the stoppers off and insert a glowing splint into each tube

Results:

In test tube A (the experiment) – the glowing splint dies out, therefor no oxygen is present, and it had all been used by the germinating seeds to respire.

In test tube B (the control) – the glowing splint ignites, therefor proving that there is oxygen present since the dead beans are unable to respire by making use of the oxygen.

Investigation 2: carbon dioxide is produced during aerobic respiration:

Aim: To prove that carbon dioxide is produced during aerobic respiration

Soda lime can be used to remove carbon dioxide from the atmosphere and sodium hydroxide can be used to remove carbon dioxide from liquids or solutions

Method:

1.

Use a small organism – that can produce carbon dioxide through aerobic respiration

2.

Sterilize the equipment so that no microorganisms influence the results

3.

Place snail into large jar

4.

Set up the apparatus and tightly seal the tubes to ensure that no outside air enters and affects the results

5.

Examine test tubes the following day to ensure that enough time is provided for aerobic respiration to take place

Results:

In test tube B – the lime water remains clear, carbon dioxide is removed by the sodium hydroxide and the soda lime

In test tube D – the lime water turns milky due to carbon dioxide produced by the snail

Conclusion: carbon dioxide is produced during aerobic respiration by living organisms

Cotton wool stopper:

Rubber stopper:

1.

Airtight seal

2.

Flexible and secure

3.

Prevents contamination

In essence a rubber stopper would be used for an airtight seal and a cotton wool stopper would be used when protecting the content but still allowing for gas exchange

Investigation 3: Carbon dioxide is produced during anaerobic cellular respiration:

Aim: to prove carbon dioxide is produced during anaerobic respiration

Method:

1.

Sterilize the equipment so that no microorganisms can affect the results

2.

Boil the sugar solution (serves as food source for yeast) in advance to ensure that all the oxygen is removed from the solution and it kills any remaining microorganisms present in the solution

3.

The yeast and sugar solution (will lead to alcoholic fermentation) should be in test tube A and the clear lime water should be in test tube B

4.

Cover the sugar solution with a thin layer of paraffin so that no oxygen from the air can dissolve into the solution, make sure that the test tube is tightly sealed so that the outside air cannot interfere with the results

5.

The apparatus should be placed in a warm water bath because yeast grows quickly in warm conditions, record results in few hours

Results:

The clear lime water becomes milky in color

Conclusion: carbon dioxide is produced during anaerobic respiration in living cells

Three stages of aerobic respiration:

-

Glycolysis

-

Krebs cycle

-

Oxidative phosphorylation

Glycolysis:

1)

It takes place outside of the mitochondrion, in the cytoplasm of the cell

2)

No oxygen is required within this phase

3)

Glucose is broken down into smaller molecules, releasing a small amount of energy that is stored in energy rich ATP molecules

4)

It releases hydrogen ions that are used in the third stage of aerobic respiration, oxidative phosphorylation

Krebs cycle: (in the matrix of the mitochondria)

1)

It can only take place when oxygen is present

2)

It occurs within the mitochondrion

3)

This phase releases carbon dioxide and hydrogen ions (H+)

4)

Transports hydrogen atoms to the third stage, oxidative phosphorylation, via hydrogen carrier enzymes

5)

Pyruvic acid undergoes a series of cyclic reactions

6)

This cycle completes itself twice

Oxidative phosphorylation: (in the membrane of cristae)

1)

It takes place within the mitochondria and requires oxygen

2)

Passes high energy hydrogen atoms from one hydrogen carrier enzyme to another, releasing energy in the process

3)

It uses the released energy to combine the phosphate molecule to an ADP molecule to form ATP – this is called phosphorylation