Topic 4 — Bioenergetics

What is the word equation for photosynthesis?

carbon dioxide + water → glucose + oxygen

What is the balanced symbol equation for photosynthesis?

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Is photosynthesis an exothermic or endothermic reaction?

endothermic

What is an endothermic reaction?

Takes in energy from surroundings

• temperature of surroundings decreases

In photosynthesis how is energy transferred?

environment → chloroplasts by light

What are the factors that affect the rate of photosynthesis? (4)

• Temperature

• Light intensity

• Carbon dioxide concentration

• Amount of chlorophyll

What adaptations do the leaves of plants have that makes them well equipped for photosynthesis? (6)

• Broad leaves — large SA

• Thin leaves — short diffusion distance

• Chlorophyll in chloroplasts — absorbs light

• Veins:

  • water in xylem → cells

  • remove sugars made in photosynthesis in phloem

• Air spaces:

  • CO₂ → cells → O₂ by diffusion

• Guard cells — open and close stomata — gas exchange

What is meant by a limiting factor?

Factor that limits amount of photosynthesis a plant carries out

What is the effect on photosynthesis when you increase the light intensity?

Increases rate until another factor is limiting

Why does this graph of light intensity against the rate of photosynthesis level off?

Light no longer limiting

• another factor is limiting → plant can’t photosynthesise faster

What is the effect on photosynthesis when you increase the temperature?

• Photosynthesis controlled by enzymes

• Rate increases until enzymes denature

What happens to the rate of photosynthesis when the temperature is too high (beyond the optimum)? Why?

• Enzymes denature

• Rate of reaction decreases

What effect does increasing carbon dioxide concentration have on the rate of photosynthesis?

Increases rate until another factor is limiting

Why do the carbon dioxide concentrations around a plant rise at night?

• Plant respires but no photosynthesis

• Light intensity and temperature increase in morning — CO₂ around plant used up

Why does this graph of carbon dioxide concentration against the rate of photosynthesis level off?

Another factor is limiting — plant can’t photosynthesis faster

What happens if a plant doesn’t have enough magnesium?

• Can’t produce chlorophyll — needed for photosynthesis

• Leaves turn yellow — chlorosis

• Rate of photosynthesis decreases

• As the distance of the light from the plant __________, the light intensity __________.

  • That is an _________ relationship — as one goes ____, the other goes _____.

• increases

• decreases

• inverse

• up

• down

What is the inverse square law for light intensity in the context of photosynthesis?

light intensity$\propto$ 1 / distance²

Outside, there is a constant interaction between the different factors that affect the rate of photosynthesis. For example:

• Early in the morning, ______ ________ and ______________ often limit the rate of photosynthesis.

• As light levels and the temperature rise, ________ ________ levels become limiting.

• On a bright, cold winter day, ___________ probably limits the rate of the process.

• light intensity

• temperature

• carbon dioxide

• temperature

Why would big commercial greenhouses control the temperature, the levels of light and carbon dioxide?

• Fastest rates of photosynthesis

• Plants grow quicker

What are the advantages of growing crops in greenhouses? (5)

• Fewer staff are needed — reduces costs

• Turnover is fast

  • Time from seed → harvest is shorter — more crops are possible

• Final crop is larger, cleaner, and often soil free — worth more money

• Bad/unseasonal weather doesn’t affect crops or harvesting

• No need for ploughing — crops may be grown where soil is poor

What are the disadvantages of growing crops in greenhouses? (2)

• Electricity and gas used to maintain narrow conditions is expensive

  • light

  • temperature

  • carbon dioxide levels

• Diseases could spread rapidly through the entire crop

What are the 3 ways of measuring the rate of photosynthesis in the lab?

• Rate of oxygen output

  • number of bubbles in a given time

  • measuring cylinder or gas syringe

• Rate of carbon dioxide uptake

  • data logger and carbon dioxide probe

• Rate of carbohydrate production

  • test plant leaves for starch using iodine

  • measure overall increase in the plant’s biomass

What is the independent variable in RP 6?

Light intensity

What is the dependent variable in RP 6?

Rate of photosynthesis

What are the control variables in RP 6?

• Temperature of the water

• Carbon dioxide concentration — concentration of sodium hydrogencarbonate solution

• Type of pondweed

What are the sources of error in RP 6?

• Bubbles vary in size and can form too quickly to count accurately

• Temperature changes (water or using a standard lamp) — affects the rate of photosynthesis

What are 3 ways to get a more accurate value of the oxygen produced in RP 6?

• Measuring cylinder or gas syringe — measure exact volume of gas produced

• Inverted filter funnel over pondweed — ensures all gas bubbles are caught and directed into measuring equipment

• Repeat, remove anomalies, and calculate a mean — reduces the effect of random error

Why do we use a LED light source in RP 6?

Releases very little heat — won’t affect the rate of photosynthesis

If we used a light source that emitted too much heat, what effect would it have on the experiment?

• Increases the temperature of the water

• Temperature affects the rate of photosynthesis

• Affects the results

Why do we use sodium hydrogen carbonate solution in RP 6?

• Releases carbon dioxide

• Allows pondweed to photosynthesise — carbon dioxide concentration is not a limiting factor

Why do we leave the piece of pondweed in the boiling tube for 5 minutes in RP 6?

Gives the pondweed time to acclimatise to the conditions in the boiling tube

What happens to the number of bubbles of oxygen produced per minute if you double the distance?

Number of bubbles produced per minute falls by a factor of four

In RP 6, if we double the distance, then the number of bubbles per minute falls by a factor of four.

• What is this called?

• Why does this happen?

• Inverse square law

• When the plant is moved twice as far away from the lamp, the light energy spreads out over four times the area → light intensity falls by a factor of four.

• Plant has four times less light to photosynthesise → the rate of oxygen bubbles it produces falls by four times.

Required Practical 6 — Photosynthesis:
1. Place a boiling tube 10 cm away from an ______ light source.

2. Fill the boiling tube with ________ ____________________ solution.

3. Put a piece of __________ in the boiling tube with the cut end at the ____.

• Leave this for 5 minutes

4. Once you see bubbles of _______, start a __________ and count the number of bubbles produced in one minute.

5. Repeat steps 1 - 4 two more times, remove _________, and calculate the ______ number of bubbles produced in one minute.

6. Repeat steps 1 - 5 for different ___________ (20 cm, 30 cm, 40 cm).

• LED

• sodium hydrogencarbonate

• pondweed

• top

• oxygen

• stopwatch

• anomalies

• mean

• distances

What can glucose produced in photosynthesis be used for? (5)

• Respiration

• Converted into insoluble starch → storage

• Produce fat or oil → storage

• Produce cellulose → strengthens cell wall

• Produce amino acids → protein synthesis

To produce proteins, plants also use _______ _____ that are absorbed from the ____.

• nitrate ions

• soil

What is the test for glucose (sugars)?

Benedict’s solution

What is the test for starch?

Iodine

What is the test for proteins?

Biuret reagent

Is cellular respiration an exothermic or endothermic reaction?

Exothermic

What is aerobic respiration?

Uses oxygen to release energy from glucose

What is anaerobic respiration?

Releases energy from glucose without using oxygen

How can respiration take place in cells to transfer energy?

• Aerobically

• Anaerobically

What do organisms need energy for? (3)

• Chemical reactions — build larger molecules

• Movement

• Keeping warm

What is the word equation for aerobic respiration?

glucose + oxygen → carbon dioxide + water

What is the balanced symbol equation for aerobic respiration?

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

What is the equation for anaerobic respiration in muscles?

glucose → lactic acid

Why is less energy transferred in anaerobic respiration than in aerobic respiration?

Incomplete oxidation of glucose

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

glucose → ethanol + carbon dioxide

What does fermentation have economic importance in the manufacture of?

• Bread

• Alcoholic drinks

What is fermentation?

Anaerobic respiration in yeast cells

What does the number if mitochondria in a cell tell you?

How active the cell is

How are mitochondria adapted for aerobic respiration?

• Folded inner membrane → large SA

  • for enzymes

• During exercise the human body reacts to the increased demand for energy.

What increases during exercise and why?

• Heart rate

• Breathing rate

• Breath volume

  • provide muscles with more oxygenated blood

During exercise, what happens if insufficient oxygen is supplied to the muscles?

Anaerobic respiration

During anaerobic respiration in muscles, what does the incomplete oxidation of glucose cause?

A build up of lactic acid → oxygen debt

What happens during long periods of vigorous activity?

Muscles become fatigued → inefficient contraction

What does the body do to reduce the build up of lactic acid from anaerobic respiration?

Blood flowing through muscles transports lactic acid to the liver — converted back into glucose

What is oxygen debt?

Amount of extra oxygen needed after exercise → reacts with lactic acid and removes from cells

What is the equation for oxygen debt repayment?

lactic acid + oxygen → carbon dioxide + water

Fully explain the increase in heart rate during exercise. (5)

• Heart rate increases — pumps greater volume of oxygenated blood → muscles

• Delivers faster and greater supply of oxygen + glucose

• Increased rate of aerobic respiration

• Releases more energy — used for muscle contraction

• Faster blood flow:

  • removes carbon dioxide from muscles more quickly

  • removes lactic acid more rapidly — prevents oxygen debt + muscle fatigue

Fully explain the increase in breathing rate during exercise.

• Breathing rate + breath volume increase — brings more air and oxygen to lungs

• Allows more oxygen to enter blood → delivered to muscles

• Muscles use extra oxygen to increase rate of aerobic respiration

• Increased respiration releases extra energy — muscle contraction

• Faster breathing rate — removes carbon dioxide from blood more quickly

  • carbon dioxide must be removed — waste product continuously produced by increased rate of respiration

During exercise, why is the glycogen stored in the muscles converted back to glucose?

• Muscles need lots of extra energy to contract

• Glycogen converted back to glucose — extra energy

• Increases rate of respiration

What is metabolism?

Sum of all reactions in a cell or the body

How is the energy transferred by respiration in cells is used by the organism?

Continual enzyme controlled processes of metabolism — synthesise new molecules

What does metabolism include? (5)

• Conversion of glucose → starch, glycogen, and cellulose

• Formation of lipid molecules from molecule of glycerol and three molecules of fatty acids

• Use of glucose and nitrate ions to form amino acids — used to synthesise proteins

• Respiration

• Breakdown of excess proteins — forms urea for excretion

• Figure 8 shows an axolotl.

Explain why an axolotl may die in water with a low concentration of oxygen. [4 marks]

• Concentration gradient of oxygen is shallower

• Less oxygen diffuses into blood

• Less aerobic respiration occurs → less energy released so less metabolism