B4- Bioenergetics

Question 1

What is photosynthesis?

Answer 1

A process in plants which uses solar energy to react carbon dioxide and water to form glucose and oxygen.

Question 2

Where does photosynthesis take place, and how do plants take in energy for it?

Answer 2

In chloroplasts in green plant cells. Chloroplasts contain pigments (like chlorophyll) that absorb light. Energy is transferred to the chloroplasts by light.

Question 3

Energy is transferred to plants, from the environment, in what form?

Answer 3

Light / solar energy.

Question 4

What type of reaction is photosynthesis?

Answer 4

Endothermic (energy is transferred to plants, from the environment).

Question 5

What is the word and symbol equation for photosynthesis?

Answer 5

Carbon dioxide + water →light→ glucose + oxygen

6CO₂ + 6H₂O →light→ C₆H₁₂O₆ + 6O₂

Question 6

In what 5 main way do plants use glucose?

Answer 6

1. Respiration (to generate energy that allows the plant to convert the rest of the glucose to the below substances)
2. Making cellulose (for cell walls)
3. Making amino acids (to make proteins)
4. Converted to lipids (oils or fats) for storing in seeds
5. Stored as starch (for a source of energy in the winter etc)

Question 7

What is glucose combined with to make amino acids, and what is it then turned into?

Answer 7

Combined with nitrate ions, which are absorbed from the soil.

The amino acids are then made into proteins.

Question 8

Where do plants store lipids?

Answer 8

In seeds.

Question 9

What is cellulose used for in plants?

Answer 9

Making strong cell walls.

Question 10

Where is starch stored in plants?

Answer 10

Roots, stems and leaves.

Question 11

Why do plants store starch?

Answer 11

It is a source of stored energy ready for when photosynthesis isn’t happening, like in winter.

Question 12

Why do plants store energy as starch, rather than glucose?

Answer 12

Starch is insoluble, which is better for storing; a cell with lots of (soluble) glucose in it would draw in lots of water and swell up.

Question 13

What are the 3 main limiting factors of photosynthesis? Name one other potential factor.

Answer 13

1. Light
2. CO₂ concentration
3. Temperature

Chlorophyll can also be a factor.

Question 14

How could chlorophyll be a limiting factor of photosynthesis?

Answer 14

The amount of chlorophyll in a plant can be inhibited by disease, or a lack of nutrients.

These things can damage chloroplasts themselves, or cause leaves to drop off - both scenarios limiting the amount of chlorophyll produced.

The rate of photosynthesis is therefore reduced, as the plant can’t absorb as much light.

Question 15

Why is temperature a limiting factor of photosynthesis?

Answer 15

1. If the temperature is low, the enzymes needed for photosynthesis work more slowly.
2. If the plant gets too hot (around 45°C), the enzymes become damaged. Other reactions can also be affected.

Question 16

Describe how you would investigate the effect of light intensity on the rate of photosynthesis.

Answer 16

1) Place a boiling tube a specific distance away from an LED light source (doesn’t release much heat).
2) Fill the tube with water or sodium hydrogencarbonate solution (releases CO₂) and place a piece of pondweed in it.
3) Connect the boiling tube, using a bung, to a waterfilled capillary tube and syringe.
4) Use the syringe to draw the oxygen bubble in the tube alongside a ruler and measure its length.
5) Controls = temperature and time given to photosynthesise.
6) Do several readings to get a mean.
7) Repeat with varying distances between the tube and light source.
8) Use the inverse square law to calculate the change in light intensity for each experiment.

Question 17

Give the law that links light intensity and distance.

Answer 17

The inverse square law:

Light intensity is inversely proportional to the square of the distance.

In other words, light intensity = 1/d².

Question 18

How do farmers make sure temperature isn’t a limiting factor of photosynthesis?

Answer 18

Growing plants in greenhouses, which trap the sun’s heat.

Question 19

How do farmers make sure carbon dioxide isn’t a limiting factor of photosynthesis?

Answer 19

Using paraffin heaters to heat greenhouses. As the paraffin burns, it produces CO_2.

Question 20

What is respiration?

Answer 20

The process by which energy is transferred from the breakdown of glucose; it happens in every cell. All living things respire.

Question 21

What type of a reaction is respiration?

Answer 21

Exothermic.

Question 22

Give 3 examples of how organisms use energy transferred by respiration.

Answer 22

1. Synthesising and breaking down large molecules.
2. Contracting muscles.
3. In mammals and birds: to keep their bodies constantly warm.

Question 23

1. What is aerobic respiration?
2. What is anaerobic respiration?

Answer 23

1. Respiration using oxygen: the most efficient way to transfer energy from glucose.
2. Respiration w/o oxygen: the incomplete breakdown of glucose into lactic acid.

Question 24

Where does aerobic respiration happen?

Answer 24

The mitochondria.

Question 25

Where does anaerobic respiration happen?

Answer 25

The cytoplasm.

Question 26

Give the word and symbol equation for aerobic respiration.

Answer 26

Glucose + oxygen → carbon dioxide + water

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

Question 27

What is the word equation for anaerobic respiration in humans?

Answer 27

Glucose → lactic acid (+ energy)

Question 28

When and why do cells start to respire anaerobically?

Answer 28

When you do vigorous exercise and your body can’t supply enough oxygen to your muscles, cells start to anaerobically respire as well as aerobically.

Question 29

Why is anaerobic respiration undesirable and only used by body cells in emergencies?

Answer 29

1. It doesn’t transfer nearly as much energy as aerobic respiration, because glucose isn’t fully oxidised.
2. It causes lactic acid to build up in the muscles, which is painful.

Question 30

What is the name given to anaerobic respiration in yeast cells?

Answer 30

Fermentation.

Question 31

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

Answer 31

Glucose → ethanol + carbon dioxide

Question 32

Give two industrial uses of fermentation.

Answer 32

1. Bread making: the carbon dioxide released from fermentation makes bread rise.
2. Making alcoholic drinks, e.g. beer and wine: fermentation produces ethanol.

Question 33

What is metabolism?

Answer 33

The sum of all the chemical reactions occuring in an organism.

Question 34

Give 6 examples of metabolic reactions which make larger molecules from smaller ones, or that break larger ones down into smaller ones.

Answer 34

1. Glucose ⇌ starch (plants)
2. Glucose → cellulose (plants)
3. Glucose ⇌ glycogen (animals)
4. Glycerol + 3 fatty acids ⇌lipids
5. Glucose + nitrates ⇌ amino acids
6. Amino acids ⇌ proteins

Question 35

When you exercise, your muscle cells need more energy from respiration to contract. How does your body increase the amount of oxygen that gets to your cells?

Answer 35

1. Breathing rate and depth increases (to get more oxygenated blood to cells)
2. Heart rate increases (to get oxygenated blood to cells quicker, and to remove CO₂ quicker)

Question 36

What can long periods of exercise cause?

Answer 36

Muscle fatigue, where muscles get tired and stop contracting efficiently.

Question 37

Explain what an oxygen debt is and what it is caused by.

Answer 37

After cells have respired anaerobically, your body needs a certain amount of oxygen (known as an oxygen debt) to react with the buildup of lactic acid to remove it from cells (forming CO₂ and water).

Question 38

Give 2 ways in which the body removes the buildup of lactic acid which results from anaerobic respiration.

Answer 38

1. Oxygen reacts with lactic acid to remove it from cells (forming CO2 and water).
2. Blood transports lactic acid to the liver, where it is converted back to glucose.

Question 39

How does the body “repay” its oxygen debt?

Answer 39

• Breathing rate and depth remains high to get more oxygen to the blood and to cells
• You continue to breathe hard until all the lactic acid has been converted to CO₂ and water

Question 40

How could you measure breathing rate?

Answer 40

By counting the number of breaths taken in a certain period of time.

Question 41

1. How could you measure heart rate?
2. How could you reduce the effect of any random errors in your results?

Answer 41

1. Counting the number of pulses on your wrist/neck in one minute.
2. Do the experiment as a group and calculate the average pulse rate.