Water is important for plants. There are pores in the surface of the leaf, which are formed by guard cells. Changes to the guard cells cause the pores to open or close. The diagram shows guard cells, at the same time of day, from a wheat plant without water stress and from a wheat plant that has water stress. When a plant is not given sufficient water, for a period of time, it develops water stress. This can have several effects on the plant. *(c) The graphs show three more effects of water stress on wheat plants. Graph A shows the effect of water stress on percentage survival rate. Graph C shows the effect of water stress on root length. Deduce how water stress could affect the growth of wheat plants. Use information from the whole of Question 6 and your own knowledge to support your answer. 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Biology

IGCSE&ALevel

EDEXCEL

Exam No：wbi12-01-que-20240518 Year：2024 Question No：6(c)

Answer:

Answers will be credited according to candidate's deployment of knowledge and understanding of the material in relation to the qualities and skills outlined in the generic mark scheme.
The indicative content below is not prescriptive and candidates are not required to include all the material indicated as relevant. Additional content included in the response must be scientific and relevant.
- there \{is a lower (percentage) survival rate / are fewer plants\} when there is water stress / converse
- plants with water stress have a lower cellulose content / converse
- plants with water stress have \{a smaller root length / roots that are 4.5 cm smaller\} / converse
- plants with water stress have lower chlorophyll content / converse
- relevant comment regarding validity of data / significant difference between the groups
- lower cellulose content results in \{\{thinner/ weaker\} cell walls / fewer cells / reduced tensile strength\} / converse
- \(\quad\) thinner cell walls / reduced calcium pectate\} will result in less growth due to less support (for plants) / converse
- smaller roots will absorb \{less water / fewer mineral ions\} in plant / converse
- fewer magnesium ions results in reduced chlorophyll formation
- fewer nitrates' results in reduced \{amino acid / protein / chlorophyll / DNA\} formation
- fewer calcium ions results in reduced \{calcium pectate / middle lamella\} formation
- less water results in \{reduced photosynthesis / reduced metabolic reactions / increased wilting of plant / reduced turgidity / closure of stomata / reduced transpiration / less uptake of mineral ions\}
- reduced chlorophyll results in \{fewer chloroplasts / less light absorption / reduced photosynthesis\}
- reduced photosynthetic rate results in reduced production of named photosynthetic product e.g. glucose
- reduced \(\beta\)-glucose results in reduced cellulose formation / reduced a-glucose linked to reduced respiration
- reduced \{protein synthesis / photosynthetic products / mitosis\} would result in decreased \{growth / seed production / yield\} of plants

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