Metabolism + photosynthesis pracitcal

Question 1

Define metabolism

Answer 1

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

Question 2

What is the energy transferred by respiration in cells used for

Answer 2

The energy transferred by respiration in cells is used by the organism
for the continual enzyme controlled processes of metabolism that
synthesise new molecules

Question 3

What is the energy released by respirations used for

Answer 3

the energy released by respiration is used by enzymes to synthesise new molecules in the cell

Question 4

Examples of metabolic reactions

Answer 4

• conversion of glucose to starch (storage form of glucose in plants - conversion takes place in plants), glycogen (storage form of glucose in humans - this conversion takes place in humans and other animals) and cellulose (strengthens the plant cell wall)
• the formation of lipid molecules from a molecule of glycerol and three
  molecules of fatty acids (it occurs Pancreas, small intestine) -lipids are found in the cell membrane
• the use of glucose and nitrate ions to form amino acids which in turn are used to synthesise proteins
• the reactions of respiration

the reactions of photosynthesis

• breakdown of excess proteins to form urea for excretion by the kidneys.

Question 5

Metabolic reactions are controlled by _____

Answer 5

Metabolic reactions are controlled by enzymes

Question 6

Describe how to investigate the effect of light intensity on the rate of photosynthesis

Answer 6

Take a boiling tube and place it a specific distance away from an LED light source.

An LED light is used as these do not release very much heat.
Too much heat would change the temperature of the experiment

Now fill the boiling tube with sodium hydrogen carbonate solution
This chemical releases CO2, which is needed for photosynthesis

Put a piece of pondweed into the boiling tube with the cut end at the top.
Leave this for five minutes to acclimatise to the conditions in the boiling tube

As the pondweed photosynthesises, bubbles of oxygen gas will be produced from the cut end of the pondweed. The oxygen released will collect in the capillary tube

At the end of the experiment, 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.

This is proportional to the volume of O2 produced.

Repeat the experiment twice with the light source at the same distance, to calculate the mean volume of O2 produced

Repeat the entire experiment with the light source at different distances from the pondweed

Question 7

Describe and explain the results of the photosynthesis experiment

Answer 7

If we double the distance, the then the volume of bubbles per minute falls by a factor of four.

This is because of the the inverse - square law.
The results are because, if you double the distance between the light and your plant, light intensity falls by a factor of four. Because light is needed for photosynthesis, it also causes the number of oxygen bubbles to fall by four times

light intensity ⍺ 1/distance²

Half a U shape

Question 8

calculate the light intensity when the lamp is 10cm from the pondweed

Answer 8

light intensity ⍺ 1/distance²

light intensity = 1/10^2

light intensity = 0.01 arbitrary units