Photosynthesis, Respiration, Movement Of Water and Minerals In Plants

Question 1

4.11 State the equation for photosynthesis in words

Answer 1

Photosynthesis is the process in the chloroplasts by which plants use chloropyll to trap light energy from the sun, convert it into chemical energy and use it to produce food in the form of carbohydrates such as sugars and starch. The raw materials are carbon dioxide and water. Oxygen is released as a waste product

Carbon dioxide + water → (chlorophyll + light energy) sugars + oxygen + water

Question 2

4.12 List the seven environmental factors that affect the rate of photosynthesis

No details of wavelength absorption and action spectra are required

Answer 2

State the seven environmental factors affecting photosynthesis include:

1. Temperature
2. Light Intensity
3. Light quality (Photosynthetically Active Radiation PAR = visible light)
4. Light duration
5. Carbon dioxide
6. Water
7. Mineral nutrients

Question 3

4.13 Describe how environmental factors affect the rate of photosynthesis; to include ‘Law of Limiting Factors’ and how growers can optimise the conditions for photosynthesis

No details of methods are required

Answer 3

‘Law of Limiting Factors’ : states that the factor in least supply will limit the rate of photsynthesis.

Careful consideration need to be given to cost & waste implicationswhen attempting to influence the rate of photsynthesis (temp, light intensity, light quality, light duration, water carbon dioxide, mineral nutrients)

Question 4

4.13a Describe how the environmental factor temperature can affect the rate of photosynthesis and how growers can optimise the conditions for photosynthesis

No details of methods are required

Answer 4

• Description: Enzymes assist in the production of photosynthesis. Enzyme activity increases with temperature from 0^oC-36^oC and cease to function at 40C+ when enzymes breakdown. This patter is mirrored by the effect of air temp. on the rate of photosynthesis which increases with rising temp up to an optimum (which varies between species from 25^oC to 36^oC) above which it slows again. At high temps stomata may close to reduce water loss preventing Carbon dioxide uptake. Very high temps leaves may be damaged and photosynthesis cease altogether.
• Grower Optimisation: Lower seasonal temperatures can be raisedby growing plants under protection in glass houses / poly-tunnels with a heat source. e.g. thermostatically controlled heaters, parrafin heaters. Insulation by be used e.g. bubble wrap on a small scale.
• Grower Optimisation Excessive heat can be mitigated by shading to reduce the solar gain including blinds, netting or washes applied to glass, ventilation and damping down (speading water in the protected environment to evaporate, increasing the humidity and reducing the chance of temperature stress on the plants

Question 5

4.13b Describe how the environmental factor light intensity can affect the rate of photosynthesis and how growers can optimise the conditions for photosynthesis

No details of methods are required

Answer 5

light energy fules the reactions tacking place in photosynthesis. Therefore the amount of light energy available is important in determining the rate of photsynthesis.

Description: light intensity the more light, the great the light intensity supplied to the plant , the more photosynthesis can take place. Beyound the optimum light intesit the rate of photsynthesis levels off as the chloroplasts are fully engaged. This is called the saturation point. and varies from species to species.

Stomatas close as light leves decrese, there by reducing the uptake of CO2

Grower Optimisation: Care must be taken to ensure glass is clean / and condensation is avoided as these would reduce light transmition . Light intensity can be increased by using artificial light (Supplementary Lighting) to boost light levels. particularly in winter when light is the rate-limiting factor in temperate climates.

Question 6

4.13c Describe how the environmental factor light quality can affect the rate of photosynthesis and how growers can optimise the conditions for photosynthesis

No details of methods are required

Answer 6

Description: Duration of light is directly linked to the rate of photsynthesis. Seasonal variations increasingly longer in from mid winter to midsummer , and decresing from midsummer to midwinter

Grower Optimisation: supplementary lighting necessary to extend the day in winter with its short days.

Question 7

4.13d Describe how the environmental factor light quality can affect the rate of photosynthesis and how growers can optimise the conditions for photosynthesis

No details of methods are required

Answer 7

Description: light quality is important to optimising photosynthesis. Photsynthesis only utilises certain light wavelengths (red & blue parts of the visable spectrum) Chloroplasts absorbe the light that is useful for photsynthesis and reflect the rest which is why we see plants as green.

Grower Optimisation: If supplementary light is used the grower must ensure that the not only is the light inessity sufficient bu that the light given off must produce light with the correct wavelenghts to enable photsynthesis ( know as photosynthetically active radiation)

Question 8

4.13f Describe how the environmental factor water can affect the rate of photosynthesis and how growers can optimise the conditions for photosynthesis

No details of methods are required

Answer 8

Description: Water is required for photosynthesis reaction but this requirement is only a small part of the total water taken up by a plant. A constant water supply up the xylem to the leaves is needed to maintain leaf tugidity (ie keeping leaf surface area optimised for photosynthesis). Similarly constant water supply is needed to keep stomata open thereby enabling CO2 uptake. If leaf water content falls below 90% optim then stomata will close to minimise further waterloss. Such stomata closure can reduce the rate of photsynthesis by as much as 50%. Corresponding changes in leaf position, due to wilting, will result in an associated decrese in light interception. A visibilty wilting plant will be hardly photosyntheising at all. Therefore it is essential that water is supplied at the correct rate to optimise growth.

Excessive soil water, known as ‘water-logging’ leads to anerobic conditions around the roots of plants which may cause root tissue to decompose. This typically starts at the tips of the roots, and leads to stalled growth and plant development. If water-logging persists it can lead to plant death

Grower Optimisation: to increase the amount of water there are a wide range of options which vary due to scale: Hydroponic growing systems, electronically controlled irrigation systems, air humidifying systems, field irrigation, rain water harvesting, to watering can and manual pressure sprayer for smaller scale

Grower optimisation: excessive water levels can be mitigated by improving drainage though digging open ditches, french ditches (aggregate filled), piped drains, installing raised beds, and the use of containers (plant pots) to raise plants. addition of soil conditioners to

Question 9

4.13e Describe how the environmental factor Carbon Dioxide can affect the rate of photosynthesis and how growers can optimise the conditions for photosynthesis

No details of methods are required

Answer 9

Description:

• CO2 level immediatly arround plants can fall if planting is very dense
• CO2 Level call fall if plants have bee photosynthesising very rapidly in an enclosed space such as an unventilated greenhouse

Grower Optimisation: atmosphere in protected environments can be enriched by supplying CO2 at leves above that found naturally in the atmosphere. Increased in rate of photsynthesis increses yield and quality

Question 10

4.13g Describe how the environmental factor mineral nutrients can affect the rate of photosynthesis and how growers can optimise the conditions for photosynthesis

No details of methods are required

Answer 10

Description: Mineral nutrients are required by the leaf to produce chlorophyll pigment. Production of chlorphyll must be continuous since it looses it effeciency quickly. A plant deficient in iron, nitrogen or magnesium especially turns yellow chlorotic and loses much of it photosynthetic ability.

Variegated leaves have lower rates of photsynthesis, and such plants will have a slower growth rate.

Grower Optimisation: Application of ferilizers to areas such as lawn and vegeatable plot is necessary to prevent mineral nutrient defficientys occuring as harvesting / mowing means nutrients are not returned to the soil. Similarly plants in conainers will eventually depleate the nutrients in the growing medium so a feeding regieme will be needed.

Question 11

4.21 State the equation for aerobic and anaerobic respiration in words

Answer 11

Respiration is the process by which the products of photosynthesis are broken down in a controlled way to release energy for use in the plant. Respiration place in the mitochondria of cells, oftened termed ‘cellular respiration’

Aerobic respiration: sugars + oxygen → water + carbon dioxide + high yield of energy (ATP + Heat)

Anaerobic respiration takes place in the absence of oxygen. It is comparatively inefficient, taking place in the cytoplasm of the cells. Resulting in an incomplete breakdown of the carbohydrates which produces enthanol as a waste product. Extended periods of aerobic respiration lead to a build up of enthanol which can prove toxic and cause root death. Anaerobic conditions can be advantageous, allows plants to survive periodic flooding. Similarly utilised to extend seed storage. In fruit and veg storage it helps prevent senescence onset and loss of quality

Anaerobic respiration: sugars → ethanol + carbon dioxide + low yield of energy (ATP + Heat)

Question 12

4.22 List the two factors that affect the rate of respiration

Answer 12

The two factors that affect the rate of respiration are

1. oxygen
2. temperature

Question 13

4.23 Describe how oxygen and temperature affect the rate of respiration

Answer 13

oxygen affects the rate of respiration:

• oxygen is needed for aerobic respiration. oxygen must be present for the complete break down of carbohydrate and to maximise energy release

temperature affects the rate of respiration by:

• enzymes are involved in the reactions during respiration. The rate of respiration therefore increases upto an optimum, beyond which the rate decreases temperature.

Question 14

4.24a Describe the significance of anaerobic and aerobic respiration in water logging

Answer 14

Waterlogging: plants need oxygen in the soil to enable the root system to develop optimally. Plant roots in waterlogged soil, will be deprived of oxygen and therefore forced to respire aerobically, this allows plants to survive temporary inundations. Anerobic respiration may lead to a build up of enthanol in the root tissue which may check the plants growth. If the waterlogging is persistant then the root tissue may die due to a toxic build up of ethanol within it, which may lead to the death of the whole plant.

Question 15

4.24b Describe the significance of anaerobic and aerobic respiration in propagation

Answer 15

propagation: High rate of respiration is desirable in the propagation of cuttings and seed germination as new cell production needs plenty of energy, additional heat may be used to increase the rate of respiration. Cuttings stored at low temperaturesroot more readily. Strawberry runners kept in cold storees over winter maintain heir quality and are also stimulated to flower the following year.

Question 16

4.24c Describe the significance of anaerobic and aerobic respiration in produce storage

Answer 16

produce storage: low rates of respiration are required to delay the ripening and senescence in storded produce such as fuit, vegetables and cut flowers. Temperatures are reduced and controlled atmospheres are utilised to reduce the rate of respiration. Growers, distributors, retailers and consumers have produced as ‘cool chain to ekkp goods between 0-10C reducing waste and enabling longer shelf life

Question 17

4.24d Describe the significance of anaerobic and aerobic respiration in seed storage

Answer 17

seed storage: respiration in stored seeds must be kept low to prevent germination and a build up of heat which would kill the embryos. This is typically achieved by keeping moisture and temperature leves low. Most seeds can be dried to 5% moisture without damage. Seeds in cold and dry storage will last significantly longer than those in warmer and wetter conditions.

Question 18

4.13a Distinguish between diffusion and osmosis to include:

• gaseous diffusion
• liquid diffusion
• transpiration
• water uptake

Answer 18

Diffusion: process whereby molecules of a liquid or gas move from an area of high concentration to an area of lower concentration of the diffusing substance

• gaseous diffusion - Carbon dioxide and oxygen moment into and out of the leaf during photosynthesis and respiration
• transpiration -movement of water vapour

Osmosis: the movement of water from a high water (low solute) concentration to a lower water (high solute concentration) across a selectively permeable membrane

• liquid diffusion - osmosis is a special kind of diffusion where water is the diffusing substance
• water uptake is by osmosis

Question 19

4.13b Identify examples of diffusion in plants to include transpiration and gaseous exchange

Answer 19

Diffusion:

1. movement of water vapour during transpiration
2. movemnt of carbon dioxide into the leaf during photosynthesis
3. movemnt of oxygen out of the leaf during photsynthesis

Question 20

4.31c Identify examples of osmosis in plants to include:

• water uptake into cells
• turgor
• cell expansion

Answer 20

osmosis

• water uptake into cells, take place in root hairs (root epidermis cells) causing the cell to swell
• turgor pressure is the force of the water in the swolen cell pushing outwards. Tugor pressure is very important in providing support to young plants and non-woody herbaceous plants.
• cell expansion in new cells is due to turgor pressure

Question 21

4.32a Describe the pathway of water movement from the soil through the plant into the atmosphere

Soil water

Answer 21

Soil water: pathway across the root

Soil water enters the root by passing through the cell walls than across the cell membranes and into cells by osmosis. Cell wall is permeable, however the cell membrane is selectively permeable, allowing water and selected disolved molecules to pass through. The plant typically maintains a greater concentration of solutes inside the cell compared with the soil water outside the cell. Since the water concentration is greater outside the cell than inside, water will move in by osmosis. The greater the difference in concentrations of water, the faster watermoves into the root cells.

• Initially water crosses the epidermis predominantly entering the root hair cells by osmosis, some also enters by passing between the epidermal cells through the relatively porous cell walls.
• Water passes into the cortex layer, here water movement is relatively unrestricted as it moves through the intercellular spaces and lattice work of cell walls. Although some will also pass by osmosis from cell to cell
• flow through root cell walls
• before reaching the stele, the central vascular region, water must cross the endodermis, a single layer of cells that control the passage of water and solutes into the stele. A waxy strip forming part of the cell wall of the endodermal cells (Casparian strip) prevents water from moving between the cells and all water is forced to pass accorss the endodermal cell membranes and into the cells by osmosis. Mineral uptake is also controlled by the endodermis, as only certain minerals are able to cross it. Water passes through the endodermis and pericycle to the xylem which transports the water and solutes upto the stem and leaves above.

Question 22

4.32b Describe the pathway of water movement from the soil through the plant into the atmosphere

Transport through xylem of stem

Answer 22

Transport through xylem of stem:

(transpiration pull)

Water is ‘sucked’ up the xylem tissue of the stem by a process called transpiration pull. As water is lost from the leaves, it is replaced by water which is drawn up the stem carrying disolved minerals with it. Evaporation of water from leaf cells means that to stay turgid, which is important for optimal photosynthesis, the water lost must be replaced by water in the xylem. Pressure is created in the xylem and water moves up through the stem and leaf petiole by suction as long as wateforms a continuous column. If the water column in the xylem is broken, air moves into the xylem and may restrict the further movement of water.

Question 23

4.32c Describe the pathway of water movement from the soil through the plant into the atmosphere

Pathway across leaf

Answer 23

Pathway across leaf:

• xylem in veins distributes water and solutes across the leaf
• osmosis across leaf cells
• flow between leaf cell walls
• evaporation from leaf cell walls into mesophyll spaces,

Question 24

4.32d Describe the pathway of water movement from the soil through the plant into the atmosphere

Diffusion through stomata of leaf

Answer 24

Diffusion through stomata of leaf

from where the water vapour diffuses out of the leaf into the surrounding air through the stomatal pores, due to the relatively lower humidity in the surrounding aircompared with the leaf inside

Question 25

4.32e Draw a diagram showing the pathway of water movement from the soil through the plant into the atmosphere

Answer 25

Diagram

Question 26

4.33 State what is meant by the term ‘transpiration’

Answer 26

Transpiration:

is the evaporation of water vapor from stomata in their leaves and other plant surfaces

Question 27

4.32 List the 3 factors that affect the rate of transpiration

Answer 27

List the factors that affect the rate of transpiration:

1. Relative Humidity: if air surrounding leaf is very humid the rate of water vapor diffusion and transpiration drops, conversly moving air will decrease the relative humidity and increase the rate of transpiration
2. Temperature: effects the rate at which water vapour evaporates and diffuses. As temperatures rise, diffusion is sped up to a maximium, whereby the high temperatures result in stomata closure and transpiration ceases.
3. Wind Speed: Transpiration is faster in windy conditions

Question 28

4.34a Describe how the plant may limit water loss to include stomata closure

Answer 28

A plant may limit water lost by closing its stomata e.g.

Transpiration is due to the large pores needed for carbon dioxide uptake. Stoma consist of a central opening or pore surrounded by two sausage shaped guard cells which control their opening. When the guard cells are fully turgid the stomata remains open whereas loss of turgor in the guard cells causes them to close to reduce water loss

Question 29

4.34b Describe the 3 key ways leaves have evolved to limit water loss

One named plant should be known for each adaptation

Answer 29

Plants have evolved many adaptations to help limit waterloss

1. leaf hairs e.g. Stachys byzantina (traps humid air close to leaf surface)
2. thick cuticle e.g. Ilex aquifolium (waxy layer reduces water loss -evergreens)
3. needles e.g. Pinus sylvestris (reduced surface area and deep set stomata)

• Other plants have leaves which store water e.g. Cassula ovata
• Cacti have extream adaptations where the leve has adapted to become a spine and the stem has replaced the leaf as the site of photosynthesis and water storage e.g. Ferocactus glaucescens

Question 30

4.35a Describe the uptake and distribution of minerla nutrients in the plant

Answer 30

1) nutrients from the soil solution active uptake against concentration gradient into root cells. mineral solutes present in the soil water are absorbed by the root. At the endodermis the solutes must cross the cell membrane. Since the concentration of nutrients inside the cell is almost always greater than present in the soil water uptake is against a concentration gradient. Nutrients cannot enter the endodermis by simple diffusion and have to be taking in by a process called active transport which requires energy. This process is also selective and the plant only absorbs the mineral nutrients it requires and rejects other

transport through the plant in xylem to the leaves

redistribution through phloem to other plant organs e.g. flowers and fruits.

Question 31

4.41a Describe how the internal structure of the leaf is designed to maximise photosynthesis and minimise transpiration

This should be studies in reference to a typical dicotyledon leaf

Answer 31

Internal structure of the leaf

Maximise photosynthesis:

palisade mesophyll cells are packed together (below the epidermis) pointing downwards. The many chloroplasts within the plaisade mysophyll absorb light energy to carry out the photosynthesis process, and can move to the top of bottom of the cells depiding on light levels.

Spongy mesophyll allows two way gas exchange, Carbon dioxide is able to reach the palisade mesophyll, and oxygen (by product of photosysnthesis) is able to leave the leaf.

veins (vascular bundles) bring water and solutes in the xylem and removes sugars in the phloem.

Minimise transpiration:

Question 32

4.42 Describe how the external structure of the leaf is designed to maximise photosynthesis and minimise transpiration

This should be studies in reference to a typical dicotyledon leaf

Answer 32

External leaf strucutres

Maximise photosynthesis:

• upper epidermis, single layer of cells without chloroplasts enables light transmition to the palisade mesophyll below

Minimise transpiration:

• waxy cuticle on leaf surface to reduce water loss
• stomata predominantly found on the lower leaf area to reduce transpiration and limit transpiration