R2101 4.1 – 4.2 Photosynthesis, Respiration

Question 1

What is photosynthesis?

What is the equation for photosynthesis

Answer 1

Carbon Dioxide + Water = Sugars + Oxygen

In presence of chlorophyll and light

The chemical process used by plants, of capturing light energy‚ converting it to chemical energy‚ and storing it by making sugar.

This energy can be stored in the plant’s cells and used to fuel the plant’s functions.

Question 2

What factors affect rate of photosynthesis?

Answer 2

Light (intensity, quality/PAR & duration)

Temperature: optimum 25–30°C, minimum 5°C

Water availability: drought, flood etc stomata close and inhibit

Nutrient availability: iron and magnesium produce chlorophyll

Carbon dioxide levels

Question 3

Why is photosynthesis important?

Answer 3

Basis of all living things – capturing energy from the sun and using for all living beings

Absorbing CO2 and releasing O2 balances respiration

Question 4

What is the law of limiting factors?

Answer 4

• Where there are several variables, the factor in least supply will limit the rate of photosynthesis.
• Three factors can limit the rate of photosynthesis: light intensity, CO2 concentration and temperature.
• Constant rate of change for light and CO2; temperature plateaus at the point when the rate cannot increase any further. This is because photosynthesis is controlled by enzymes and these are sensitive to temperature.
• The peak of the temp graph would be at a higher temperature for a plant that is adapted to the desert and lower for a plant that is adapted to the arctic.

Question 5

What is the equation for aerobic respiration?

Answer 5

Oxygen + Glucose (or carbohydrate) > Carbon Dioxide, Water and Energy

Question 6

Where does aerobic respiration take place?

Answer 6

Mitochondria

Question 7

What is the equation for anaerobic respiration?

Answer 7

Glucose > Ethanol + CO2 + low energy

Question 8

What are the factors affecting rate of respiration?

Answer 8

Oxygen levels

Temperature

Question 9

What is diffusion?

Answer 9

Liquid or gas movement from area of high concentration to low concentration

Question 10

What is the definition of osmosis?

Answer 10

Movement of water from high to low concentrations across a semi-permeable membrane

Question 11

How does water get taken up from soil?

Answer 11

Osmosis through root hairs

Question 12

How does water move in the root?

Answer 12

Moves across root towards transporting tissue in centre by moving unrestricted through cell walls and intercellular spaces.

Some osmosis too.

When it meets endodermis with Casparian strip water is prevented from moving freely and has to cross the membrane which acts as a control point for mineral uptake.

Moves across endodermis, and pericycle and into xylem.

Question 13

How does water move in the leaf?

Answer 13

Out of xylem and between leaf cells

Also osmosis, as in root

Evaporates from cell surfaces and into air spaces

Water vapour diffuses out of stomata because surrounding air has lower humidity level

Transpiration

Question 14

What is the name name of the cells where photosynthesis takes place?

Answer 14

Chloroplasts, which contain the chlorophyll

Question 15

How is leaf designed for photosynthesis?

Answer 15

Green – contain chlorophyll which absorbs sunlight

Large surface area – increases surface area to allow more sunlight & carbon dioxide into the leaf

Thin – small distance for gases to travel

Stoma – allow CO2 to diffuse into the leaf and oxygen to diffuse out of the leaf

Space – in spongy mesophyll to allow gaseous exchange

Veins – contain the xylem which transport water and minerals; and phloem which transport sugars

Petiole – holding leaf to maximise light absorption

Question 16

What happens to the sugars made in photosynthesis?

Answer 16

Glucose stored as starch

Thousands of glucose molecules can be united into long chains to form starch molecules (plant food) or cellulose which is incorporated into cell walls.

Starch can later be broken down into glucose for cellular respiration or can be converted into other plant products.

Question 17

Why does increasing temperature not increase photosynthesis indefinitely?

Answer 17

Photosynthesis is controlled by enzymes and these are sensitive to temperature.

Question 18

What is PAR?

Why is it important for photosynthesis?

Answer 18

Photosynthetically active radiation

The acceptable wavelength range for photosynthesis. Plants need light in very particular parts of the spectrum, between 400 – 500 nm and 700nm.

Question 19

Why is water important for photosynthesis?

Answer 19

• The amount taken up is only a very small proportion (~10%) of the total water taken up by the plant.
• Water is important in cell turgidity and to keep stomata open. If a leaf only contains 90% of its water content then stomata will close, preventing CO2 entry. This will lead to a decrease in psn rate of 50%.
• A wilted plant will not photosynthesize at all.

Question 20

How could chlorosis be linked to poor psn?

Answer 20

• Leaves require magnesium to produce chlorophyll, the pigment in chloroplasts, which absorbs light energy.
• Plants deficient in magnesium turn yellow (chlorotic) and lose ability to photosynthesise.
• Variegation causes slower growth.

Question 21

How do greenhouse growers optimize conditions for photosynthesis?

Answer 21

1) Maximise light:

Use greenhouses constructed from glass or alternative materials that enable maximum transmission of light

Position plants for maximum light absorption

Artificial lighting systems:

• with increased light intensities
• optimum wavelengths
• lengthen a plant’s growing season
• sometimes used for the first few weeks after germination of seed, when lots of small plants can be put close together under a single light source

2) Increase the CO2 concentration:

• use paraffin heaters
• on a larger scale, use CO2 wastes from industrial processes
• can use liquid CO2, applied through pipes
• use fungi, grown as a mycelium in bags around the greenhouse, that add CO2 through their respiration
• a_tmospheric concentration_ is normally 0.03% but increasing it to 0.1% can boost yields in tomatoes by about 40%

Question 22

What happens to the sugars made during photosynthesis?

Answer 22

• Sugars: Include glucose and fructose
• Thousands of glucose molecules can be united into long chains to form starch molecules (stored plant food) or cellulose, which is incorporated into cell walls.
• Starch can later be broken down into glucose for cellular respiration or can be converted into other plant products.

Question 23

Why is PAR important?

Answer 23

Photosynthetically Active Radiation (PAR) is the acceptable wavelength range for photosynthesis.

450–550nm (blue) – for growing

600–700nm (red) – for flowers

The most effective wavelengths absorbed by chlorophyll = for psn

Question 24

What is respiration?

Answer 24

The chemical reaction that occurs within the cells of every living organism, where chemical energy is released for use

• Food energy is converted to chemical energy, which is then used for metabolic processes such as growth, development, transport, and so on.
• Respiration takes place 24–7.
• Oxygen is normally required.
• Carbon dioxide and water are produced.

Question 25

How do plants absorb oxygen?

What is the equation for aerobic respiration?

Answer 25

• Diffusion across plant tissues.
• Roots absorb oxygen via the soil atmosphere and oxygen dissolved in soil water.
• Above ground cuticle limits the entry of oxygen, but it can enter woody plants via the lenticels.

• Oxygen is supplied via the roots, the oxygen that remains in the leaf after photosynthesis and also via the lenticels.

Glucose + Oxygen –> Water + Carbon dioxide (+ Energy)

Question 26

What is ATP?

Answer 26

Adenosine Triphosphate

• = Created by mitachondria using the chemical energy released during aerobic respiration

Oxygen + Sugars –> H20 + CO2 + Released Energy

• The energy stored in ATP can then be used to drive processes requiring energy, including biological activities
• Not stored; produced ‘on the go’; the rate of synthesis must keep pace with the demand

Question 27

What’s the difference between aerobic and anaerobic transpiration?

Answer 27

Anaerobic:

Glucose –> Ethanol + CO2 + Energy

• No oxygen
• Sugar converted to ethanol rather than oxidized to CO2 and H2O
• Sugar not broken down completely so less energy produced

Question 28

Factors affecting respiration?

Answer 28

• Oxygen

• Temperature (and indirectly light)

• Water availability

• Carbon dioxide

• Kind of cell or tissue/life stage

• Seasonal growth

Question 29

What effect does temperature have on respiration?

Answer 29

• For every 10º rise in temperature, respiration rate will double, up to about 30ºC.
• Optimum temperature = 25ºC to 30ºC
• Very high temperatures, above 35ºC, will slow down with time and eventually stop as the enzymes which are involved in the process will be denatured
• The rate of respiration in a plant cell decreases when temperature decreases until respiration nearly or completely halts around freezing temperatures
• Low temperatures reduce respiration rates and help to keep fruit, veg and flowers in better quality (typically stored at temperatures of 0 – 10ºC)
• Soil temperature is also a crucial factor to consider when growing plants, particularly for germinating seeds and seedlings and when rooting cuttings. Warmer soil will equate to higher respiration rates and this translates into more root growth.