B4 - Bioenergetics

Question 1

Describe the features of a greenhouse which help provide an ideal environment for plant growth

Answer 1

Enclosed to prevent pests and diseases from providing environmental stress on the plants

Provided with a supply of artificial light to prevent light from becoming a limiting factor

Use fertilisers containing magnesium

Contain paraffin heaters to increase levels of carbon dioxide to prevent carbon dioxide being a limiting factor and provide heat

Question 2

Explain why the body changes its breathing and heart rates during and after exercise

Answer 2

During exercise, there is an increase in demand for energy so the muscles can contract more. This means that the breathing rate, heart rate and breadth volume increases to supply muscles with more oxygenated blood and glucose. This results in more aerobic respiration so there is a greater rate of energy release for muscle contraction so the body can exercise for longer as this prevents cramps and fatigue

If insufficient oxygen is supplied, anaerobic respiration occurs and the incomplete oxidation of glucose causes a build up of lactic acid which creates an oxygen debt. This means the breathing rate after exercise remains high before the blood transports the lactic acid back to the liver where it is converted to glucose

Question 3

Describe the process of photosynthesis

Answer 3

Light energy is absorbed by chlorophyll in chloroplasts in some plants/algal cells. This energy is used to convert carbon dioxide and water into glucose and oxygen

Question 4

What type of reaction is photosynthesis?

Answer 4

Photosynthesis is endothermic, because energy is transferred from the environment into the chloroplast by light

ENdothermic = energy ENtering
EXothermic = energy EXiting

Question 5

What is the word and symbol equation for photosynthesis?

Answer 5

6C02 + 6H20 —> C6H1206 + 602
Carbon dioxide + water —> glucose + oxygen

Question 6

What is a limiting factor (of photosynthesis)?

Answer 6

Factors that restrict the rate of photosynthesis if in low levels

Question 7

How does temperature affect the rate of photosynthesis?

Answer 7

As temperature increases, the rate of photosynthesis increases so temperature is the limiting factor as photosynthesis is controlled by enzymes, which gain kinetic energy as they reach optimum temperature

Above an optimum temperature, the rate of photosynthesis decreases as the enzymes denature because the active site changes shape

Question 8

How does light intensity affect the rate of photosynthesis?

Answer 8

As light intensity increases, the rate of photosynthesis increases so light intensity is the limiting factor as light provides energy needed for the reaction

After a certain point, the rate of photosynthesis stops increasing because another factor is limiting such as temperature or CO2 concentration

Question 9

How does carbon dioxide concentration affect the rate of photosynthesis?

Answer 9

As carbon dioxide increases, the rate of photosynthesis increases so it is the limiting factor because CO2 is one of the raw materials needed for photosynthesis

After a certain point, the rate of photosynthesis stops increasing because another factor is limiting, such as temperature or light intensity

Question 10

How does the concentration of chlorophyll affect photosynthesis?

Answer 10

Some plants are affected by disease, such as TMV, and environmental stress, such as magnesium deficiency. Variegated leaves have reduced chlorophyll in white areas

This affects how much light energy can be absorbed for photosynthesis

Question 11

What is the inverse square law?

Answer 11

Light intensity is inversely proportional to 1/distance²

Question 12

How can a gardener maximise photosynthesis?

Answer 12

Remove limiting factors -> gain maximum rate of photosynthesis -> increase plant yield

Profit from extra yield must be greater than the costs of providing conditions

Question 13

What are the control variables in RP6?

Answer 13

Temperature
C02 supply
Length/type of aquatic organism
Colour of light

Question 14

How can you investigate the effect of light intensity on the rate of photosynthesis?

Answer 14

Fill a boiling tube with sodium hydrogen carbonate solution and place it 10 cm away from an LED light source

Place a piece of pondweed into the boiling tube with a horizontally cut end at the top

Leave the tube for five minutes for the pondweed to acclimatise

Start a stopwatch and record the number of bubbles produced in one minute

Repeat the experiment 3 times at five different distances and calculate a mean

At a greater light intensity, more bubbles are produced, as light is needed for photosynthesis

Plot a graph of distance against number of bubbles produced

Question 15

In RP6, Why is the aquatic organism placed in a solution of sodium hydrogen carbonate solution?

In RP6, How could you test the bubbles to show they contained oxygen?

Why is counting bubbles Not an accurate way of measuring the volume of oxygen produced?

How could the method be improved to measure the rate of photosynthesis more accurately?

What is the advantage of using an LED light source?

Answer 15

To provide carbon dioxide so that it is not a limiting factor

Add a burning splint, it will buy more brightly

The bubbles are different sizes, and some bubbles can be easy to miss

Measure the volume of oxygen released in a gas syringe and increase the length of time

Does not omit a lot of infrared radiation so temperature is controlled. This is important because temperature affects the rate as photosynthesis is controlled by enzymes

Question 16

How could RP6 be modified to investigate the effect of wavelength of light on the rate of photosynthesis?

Answer 16

Place different coloured filters over the bulb

Question 17

How could RP6 be modified to investigate the effect of CO2 and temperature on the rate of photosynthesis?

Answer 17

Use different concentrations of sodium hydrogen carbonate solution

Use different temperature water baths

Question 18

What are the uses of glucose from photosynthesis? (SCARFo)

Answer 18

Used for respiration to release energy

Converted into starch for storage that can be converted back to glucose when photosynthesis is not occurring. Unlike glucose, It is insoluble so will not affect the movement of water in and out of cells by osmosis

Used to produce fat or oil for energy storage

Used to produce cellulose, which strengthens the plant cell wall

Used to produce amino acids/proteins. Glucose is combined with nitrate ions, absorbed from soil to form amino acids which are used in protein synthesis

Question 19

Describe cellular respiration

Answer 19

A series of chemical reactions that release energy from glucose

Occur continuously in all living cells and is an example of an exothermic reaction

Question 20

What are the uses of energy released in respiration?

Answer 20

In chemical reactions to build larger molecules

To keep warm

For movement, such as muscle contraction in animals or transport of substances in the phloem of plants

Question 21

What is the word and symbol equation for aerobic respiration?

Answer 21

C6H1206 + 602 —> 6CO2 + 6H20
Glucose + oxygen —> carbon dioxide + water

Question 22

What is the word equation for anaerobic respiration in muscles?

Answer 22

Glucose —> lactic acid

Question 23

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

Answer 23

Glucose —> ethanol + carbon dioxide

Question 24

Compare aerobic and anaerobic respiration

Answer 24

Aerobic respiration uses oxygen, whereas anaerobic respiration does not

In aerobic respiration, the oxidation of glucose is complete, Whereas it is incomplete in anaerobic respiration

In anaerobic respiration, the relative amount of energy transferred is high, Whereas it is low in Anaerobic respiration

Aerobic respiration forms carbon dioxide and water, whereas in anaerobic respiration in animal cells, it forms lactic acid and in plant cells and yeast cells, it forms ethanol and carbon dioxide

Question 25

Compare anaerobic respiration in plants and yeast cells with anaerobic respiration in animal cells

Answer 25

Both do not require oxygen
Both have an incomplete oxidation of glucose
Both have a relatively low amount of energy transferred

In animal cells, lactic acid is formed, whereas in plant/yeast cells, ethanol and carbon dioxide is formed

Question 26

What is the importance of anaerobic respiration in yeast?

Answer 26

Useful in the production of bread as C02 makes dough rise and ethanol evaporates

Useful in the production of alcoholic drinks as ethanol is a type of alcohol and C02 makes it fizzy

Question 27

Energy demand during exercise increases due to increased muscle contraction

How does the human body react to increased demand for energy during exercise?

Why does the human body react this way?

Answer 27

Increased heart rate to increase blood flow to muscles and lungs. Increased breathing rate so that more oxygen enters the lungs. Increased breadth volume so that more oxygen enters the lungs

To supply more blood containing more oxygen (and glucose) to muscles:
● For more aerobic respiration to release / transfer energy
● To reduce anaerobic respiration and lactic acid build up

Question 28

What happens when muscles are supplied with insufficient oxygen?

Answer 28

Anaerobic respiration takes place in muscles as the oxidation of glucose is incomplete, resulting in a buildup of lactic acid which causes:

○ Oxygen debt
○ Muscles becoming fatigued and stop contracting efficiently if activity is long and vigorous

Question 29

Define oxygen debt

Answer 29

Amount of extra oxygen the body needs after exercise to react with lactic acid formed and remove it from cells

Question 30

How is lactic acid removed?

Answer 30

Blood flowing through muscles transports lactic acid to the liver
Where it is converted back to glucose

Question 31

Define metabolism and metabolic rate

Answer 31

Metabolism is the sum of all chemical reactions in a cell or the body

Metabolic rate = the rate of these reactions

Question 32

Describe a method to investigate the effect of exercise on the body

Question 33

What are five examples of metabolic reactions?

Answer 33

The conversion of glucose into starch, glycogen and cellulose

The formation of a lipid molecule, composing of one glycerol molecule and three fatty acid molecules

The formation of amino acids from glucose and nitrate ions to synthesise proteins

Respiration

Breakdown of excess proteins to form urea for excretion

Question 34

Explain why a leaf left in the light for four days contained both glucose and starch

Explain why a leaf left in a cupboard with no light for two days did contain glucose, but did not contain starch

Answer 34

Glucose is formed in photosynthesis and excess glucose is converted to starch as storage

Starch stores have been converted to glucose so the glucose can be used for respiration because there is no light to make more glucose by photosynthesis