4. Bioenergetics

Question 1

What is the word equation for photosynthesis?

Answer 1

carbon dioxide + water ➙ glucose + oxygen.

with light above the arrow

Question 2

Where does photosynthesis take place?

Answer 2

Inside the chloroplasts. - contain chlorophyll which absorbs light.

Question 3

Is photosynthesis endo or exothermic?

Answer 3

Endothermic. Energy transferred from the environment.

Question 4

What is the symbol equation for photosynthesis?

Answer 4

6CO₂+6H₂O➙C₆H₁₂O₆+6O₂.

Question 5

What are the five main ways plants use glucose?

Answer 5

1. Respiration.
2. Making cellulose (for making strong cell walls).
3. Making amino acids (glucose combined with nitrate ions).
4. Stored as oils and fats (glucose turned into lipids for storing in seeds).
5. Stored as starch (stored in roots, stems and leaves to be used when photosynthesis is not happening).

Question 6

Why is starch better for storing (in plants) than glucose?

Answer 6

Starch is insoluble, which makes it better for storing than glucose becuase a cell with lots of glucose in would draw in loads of water and swell up.

Question 7

What is the rate of photosynthesis affected by?

Answer 7

Light intensity, CO₂ concentration and temperature.

Question 8

What is another limiting factor for photosynthesis?

Answer 8

Chlorophyll.

Question 9

What can the amount of chlorophyll in a plant be affected by?

Answer 9

Disease, environmental stress (lack of nutrients). Could cause the chloroplasts to become damaged or not make enough chlorophyll. So photosynthesis is reduced as they can’t produce enough light.

Question 10

Explain how light intensity affects the rate of photosynthesis?

Answer 10

As the light intensity increases, the rate of photosynthesis increases up until a certain point. Beyond this point CO₂ or temperature could have become limiting.

Question 11

How can you measure light intensity?

Answer 11

Using a light meter.

Question 12

Explain how CO₂ concentration effects the rate of photosynthesis?

Answer 12

As the amount of CO₂ increases, the rate of photosynthesis will increase up to a point. After this the graph flatterns out as other factors become limiting.

Question 13

Explain how temperature effects the rate of photosynthesis?

Answer 13

When the temperature is too low the enzymes needed for photosynthesis work more slowly. When the plant gets too hot, the enzymes needed for photosynthesis wil denature (at around 45°C).

Question 14

How can you investigate the rate of photosynthesis of pondweed?

Answer 14

1. Source of white light placed at a specific distance from the pondweed.
2. The pondweed is left to photosynthesise for a set amount of time. As it photosynthesises, the oxygen released will collect in the capillary tube.
3. At the end, the syringe is used to draw the gas bubble in the tube up alongside a ruler and the length of the gas bubble is measured.
4. The experiment is repeated twice with the light source at the same distance and the mean volume of O₂ produced is calculated.
5. Repeat the whole experiment with the light source at different distances from the pondweed.

Question 15

What variables should be controlled in the pondweed practical?

Answer 15

Temperature, time left to photosynthesise.

Question 16

What the inverse square law?

Answer 16

Light intensity ∝ 1/distance². When is distance increases, the light intensity decreases. They are inversely proportional.

Question 17

How do greenhouses work?

Answer 17

Trap the suns heat, making sure the temperature doesn’t become limiting. In the winter could use a heater, in the summer cold use shades and ventilation to keep the temperature at an ideal level.

Question 18

How can farmers increase the level of carbon dioxide in a greenhouse?

Answer 18

Using a paraffin heater, when it burns, carbon dioxide is made as a by-product.

Question 19

How can farmers provide minerals to plants?

Answer 19

Adding fertilisers to the soil.

Question 20

What is respiration?

Answer 20

The process of transferring energy from glucose, which goes on in every cell.

Question 21

Is respiration endo or exo thermic?

Answer 21

Exothermic - transfers energy to the environment.

Question 22

How do organisms use the energy transferred by respiration?

Answer 22

1. To build up larger molecules from smaller ones.
2. To allow the muscles to contract.
3. Mammals and birds - keep body temperature steady in colder surroundings.

Question 23

What is metabolism?

Answer 23

The sum of all the reactions that happen in a cell or the body.

Question 24

Give examples of reactions wherw larger molecules are made from smaller ones.

Answer 24

• Small glucose molecules are joined together in reactions to form starch, glycogen and cellulose.
• Lipid molecules are made from one molecule of glycerol and three fatty acids.
• Glucose is combined with nitrate ions to make amino acids, which are then made into proteins.

Question 25

Give examples of reactions where larger moleules are broken down into smaller ones.

Answer 25

• Glucose is broken down in respiration. Respiration transfers energy to power all the reactions in the nody that make molecules.
• Excess protein is broken down in a reaction to produce urea. Which is then excreted in the urine.

Question 26

What is the word equation for aerobic respiration?

Answer 26

glucose + oxygen → carbon dioxide + water.

Question 27

What is the symbol equation for aerobic respiration?

Answer 27

C6H12O6 + 6O2 → 6CO2 + 6H2O.

Question 28

Where does aerobic respiration occur?

Answer 28

Inside mitochondria.

Question 29

What is anaerobic respiration?

Answer 29

The incomplete breakdown of glucose, making lactic acid. As the glucose isn’t fully oxidised, anaerobic respiration doesn’t transfer as much energy as aerobic.

Question 30

What is the word equation for anaerobic respiration?

Answer 30

glucose → lactic acid.

Question 31

What is the word equation for anaerobic respiration in plants and yeast?

Answer 31

glucose → ethanol + carbon dioxide.

Question 32

What is anarobic respiration in yeast called?

Answer 32

Fermentation.

Question 33

Why is fermentation useful?

Answer 33

Used to make bread and alcoholic drinks. The carbon dioxide is used to make the bread rise.

Question 34

What does your body do to get more oxygen to the cells?

Answer 34

• Breathing rate and breath volume increases to get more oxygen into the blood.
• Heart rate increases to get oxygenated blood around the body faster. Removing CO2 at the same time.

Question 35

Why is it painful when doing vigorous exercise?

Answer 35

• Your body can’t supply oxygen to your muscles quickly enough so they start respiring anaerobically.
• This results in the build up of lactic acid.
• Muscle fatigue can also be caused from long periods of exercise where the muscles get tired and stop contracting effectively.

Question 36

What is an “oxygen debt”?

Answer 36

The amount of extra oxygen your body needs to react with build up of lactic acid and remove it from the cells.

Question 37

What does oxygen react with lactic acid to form?

Answer 37

CO₂ and water.

Question 38

What is another way of your body coping with high levels of lactic acid?

Answer 38

The blood that enters your muscles transports the lactic acid to the liver where it is converted bck into glucose.

Question 39

How can you measure breathing rate?

Answer 39

By counting breaths.

Question 40

How do you measure heart rate?

Answer 40

Taking the pulse.

Question 41

Why does pulse rate increase the more tense the exercise is?

Answer 41

Your body needs to get more oxygen to the muscles and take more carbon dioxide away from the muscles.