a) Describe what is meant by EACH of the following terms in relation to water movement in a plant:
i) osmosis 4 marks
ii) diffusion 2 marks
b) State FOUR functions of water in a plant. 4 marks
This question relates to the following part of the syllabus:
4.3 Describe the movement of water and minerals through the plant.
Distinguish between diffusion and osmosis to include: gaseous and liquid diffusion, transpiration, and water uptake. Identify examples of diffusion in plants, to include: transpiration and gaseous exchange.
Identify examples of osmosis in plants, to include: water uptake into cells, turgor, and cell expansion.
Describe the pathway of water movement from the soil through the plant into the atmosphere - soil water: pathway across the root (root hairs, osmosis across root cells, flow through root cell walls, endodermis); transport through xylem of stem (transpiration pull): pathway across leaf, (xylem in veins, osmosis across leaf cells, flow through leaf cell walls, evaporation from leaf cell walls into mesophyll spaces); diffusion through stomata of leaf.
DIAGRAM OF PATHWAY REQUIRED.
State what is meant by the term ‘transpiration’. List the factors that affect the rate of transpiration: relative humidity, temperature, wind speed.
Describe how the plant may limit water loss, to include: stomatal closure and leaf adaptations (hairs, thick cuticle, needles). ONE named plant example should be known for EACH adaptation.
Describe the uptake and distribution of mineral nutrients in the plant: nutrients from soil solution active uptake against concentration gradient into root cells, transport through the plant in xylem, distribution through phloem.
And also, (amongst other parts):
4.1 Describe photosynthesis and the factors that affect it.
State the equation for photosynthesis in words (carbon dioxide, water, sugars, oxygen) and state the necessity for chlorophyll and light.
List the environmental factors that affect the rate of photosynthesis: temperature, light (intensity, quality/PAR and duration), carbon dioxide, water and mineral nutrients
Part a) is directly from 4.3 and requires two straightforward descriptions. The examiners’ comments suggest the following:
i) Osmosis is the movement of water from a high water (low solute) concentration to a low water (high solute) concentration across a selectively permeable membrane.
ii) Diffusion is the movement of water molecules from an area of high water concentration to an area of low concentration e.g. loss of water vapour from the leaves in transpiration.
It is important to remember to state what the high and low concentrations are of; and not just state that it is movement from a high to a low concentration. Also, make sure you don’t get muddled between water and solute.
Part b) is looking more across the syllabus for different functions of water.
The examiners’ comments suggest the following:
· Creates cell turgor which enables cell expansion
· Controls the opening and closing of the stomata
· Supports herbaceous plants
· Enables the uptake and transport of minerals and sugars
· Is used in photosynthesis
· Dissolves substances e.g. enzymes so that they can take part in reactions
· Is essential in triggering germination
Only four functions of water are required, so set them out clearly, maybe with numbers or bullet points. Any extra functions won’t be marked, so always stick to the number asked for.