B2: Green plants as organisms

• Cell activity


• Nutrition


• Water relations and transport


• Control of growth.

Cell activity

Candidates will be assessed on their ability to:

• recall that a plant cell has a nucleus, cytoplasm and a cell membrane; it also has a cellulose cell wall, a large vacuole and (in green parts of plants) chloroplasts (B2.01)
• recognise that the co-ordinated activity of organisms results from the adaptation of cells to different functions; relate the structure of a palisade leaf cell to its function B2.02)

Nutrition

Candidates will be assessed on their ability to:

• understand that carbon dioxide and water are converted to glucose and oxygen by photosynthesis using sunlight energy absorbed by chlorophyll, the green pigment contained in chloroplasts (B2.03)
• understand that carbon dioxide from the atmosphere diffuses in through stomata and oxygen diffuses out as a result of photosynthesis (B2.04)
• explain the pattern of gas exchange between a plant and the atmosphere resulting from photosynthesis and respiration over a 24 hour period (B2.05)

• describe how the rate of photosynthesis varies with carbon dioxide concentration,light intensity and temperature; interpret data from experiments relating to photosynthesis B2.06)
• understand that plants use the glucose produced by photosynthesis for respiration to release energy, for conversion to starch for storage and to cellulose for cell walls, and as a component in protein synthesis (B2.07)
• understand the need for mineral ions for healthy plant growth, including nitrates for protein synthesis and magnesium for chlorophyll; interpret data from water culture experiments (B2.08)

Water relations and transport

Candidates will be assessed on their ability to:

• explain how water is taken in by osmosis (B2.09)
• understand the role of water in maintaining cell turgidity to support plant tissues (B2.10)
• explain the uptake of mineral ions by active transport (B2.11)
• recall that the substances required for growth and reproduction are transported within plants in xylem (water and mineral ions) and in phloem (sugars and amino acids) (B2.12)
• understand how leaf structure (shape, cuticle, palisade layer, spongy layer, veins, guard cells and stomata) is adapted for photosynthesis and transpiration (B2.13)
• explain how leaves lose water by transpiration, including the evaporation of water within the leaf and diffusion of water vapour through stomata; interpret data from experiments relating to transpiration (B2.14)
• describe how atmospheric conditions affect the rate of transpiration (B2.15)

Control of growth

Candidates will be assessed on their ability to:

• recall that auxins influence cell division and the elongation of cells at the tips of roots and shoots (B2.16)
• describe commercial applications of plant hormones: stimulating the growth of roots in cuttings; regulating the development of fruits; killing weeds by disrupting their normal growth pattern (B2.17)

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