2101 - Photosynthesis & Respiration

Question 1

Photosynthesis equation

Answer 1

Carbon Dioxide + Water + Light Energy = Sugar + Oxygen

Question 2

Respiration equation

Answer 2

Sugar + Oxygen = Carbon Dioxide +. Water + Energy

Question 3

Respiration definition

Answer 3

Respiration is the process of releasing stored energy (from Photosynthesis) within the cell for growth and cell regulation.

occurs day and night

Question 4

Aerobic respiration

Answer 4

• Conversion of Sugars and Oxygen into Carbon Dioxide and Water.
• Releases of a lot of energy.
• occurs in the mitochondria
• requires a source of oxygen, usually atmospheric

Question 5

Anaerobic respiration

Answer 5

• Does not require Oxygen
• Conversion of Sugars to Ethanol and Carbon Dioxide.
• Release a small amount of energy.
• Occurs in the Cytoplasm

Question 6

Anaerobic respiration occurs when…

Answer 6

There is not enough available Oxygen.

• Waterlogged soils
• Seeds stored in airtight storage
• Fruit in airtight storage

Short term ‘fix’ that enables energy production to continue in adverse conditions. Small energy release, also Ethanol build up which can cause tissue damage and lead to death.

Question 7

Factors affecting Aerobic respiration

Answer 7

Respiration is at its highest in actively growing cells, during seed germination or cutting producing new roots.

• Oxygen Levels, As Oxygen levels fall the rate of respiration decreases. Increase will increase in Rate of Respiration, up to a point where it will flatten.
• Temperature, Respiration is enzyme driven, therefore rates increases with temperature. Increasing past the optimum temperature will decrease the Rate of Respiration and therefore the plant will be less productive and growth slows.
• Respiration rate below 5c is very slow. Increases rapidly to an optimum around 25/30c, then decreases again due to enzyme de-activation and stops at 40c.

Question 8

Respiration in Horticultural situations

Answer 8

Reducing the Rate of Respiration in stored crops, fruit, seed and bulbs. Will keep fresh for longer.
Storage facilities may reduce temperature and replace oxygen with Nitrogen to limit the rate of respiration.

Question 9

Photosynthesis

Answer 9

Co2 + H2o + Light Energy = Sugar + o2

Occurs in the chloroplasts of plants. Typically in the leaves.
Converts co2, h2o and light into high energy sugars easily transported around the plant.

Can be efficiently converted to starch for storage (and back again when needed).

Question 10

Factors affecting Photosynthesis

Answer 10

Light
Carbon Dioxide concentration
Temperature
Water
Availability of Chlorophyll

Question 11

Law of limiting Factor

Answer 11

The factor is least supply will limit the rate of Photosynthesis.

This factor must be raised in order to increase rate of Photosynthesis. Irrespective of the availability of other limiting variables.

Horticulturalists try to optimise levels of the limiting factors to maximise production.

Question 12

Sub-Optimal, Optimal, Super-Optimal levels

Answer 12

Sub-Optimal levels, will reduce the rate of growth/productivity

Optimal levels, will allow for optimal growth

Super-Optimal levels, will typically damage the plant and reduce growth/productivity

Question 13

Factors affecting Photosynthesis - Light

Answer 13

• Low Levels have insufficient energy to drive photosynthetic reactions.
• Too little will cause Stomata to close reducing co2 exchange limiting photosynthesis
• After optimum levels are reached rate of photosynthesis flattens off.
• Too much light, can lead to bleaching/scorching and the breakdown of chlorophyll. Resulting in less growth.
  Species and situation dependant (eg desert plants or shade plants).

Question 14

Factors affecting Photosynthesis - Quality of Light

Answer 14

• Photosynthetically active radiation to harness light energy. Blue and Red end of the spectrum are most absorbed.

(artificial lighting systems)

Question 15

Factors affecting Photosynthesis - co2

Answer 15

• too little will affect rate of photosynthesis and slow growth.
• Can increase but flattens off quickly
• Too much results in an inability to respire, so growth is slowed but not directly because of photosynthesis
• add gas burner to green-house, or pump in co2

Question 16

Factors affecting Photosynthesis - Temperature

Answer 16

• optimum 25c range, rate of photosynthesis falling rapidly below 15c and dropping when it exceeds 30c. (Species dependant).

Question 17

Factors affecting Photosynthesis - Chlorophyll

Answer 17

• Lack of chlorophyll mean low rate of photosynthesis.
• normally nutrient dependant. Lack of nutrients will lead to Chlorosis in the leaf and reduced photosynthetic production.
• main nutrients needed Nitrogen, Magnesium, Iron
• Super-Optimal nutrient availability will lead to Cell Plasmolysis. Where the water in the root will move out into the soil via osmosis.
  Potentially destroying the cell and reducing growth rate.

Question 18

Factors affecting Photosynthesis - Water

Answer 18

• Optimal (field capacity)
• Shortage/drought, stomata closed and prevent gaseous exchange so no co2.
• Waterlogging, lead to aerobic respiration, leading to less energy available in the cells . And limited nutrients being absorbed by the root.