Homeostasis in plants

(a) Isolated mitochondria were used to examine respiration. • Mitochondria were taken from respiring mammalian cells and placed in a buffer solution. • Pyruvate and inorganic phosphate (Pi) were added at time zero. • ADP was added one minute later. • The oxygen concentration of the buffer solution containing mitochondria was monitored for the whole investigation. The results of the investigation are shown in Fig. 7.1.

Feb/March 2019

Sorghum and maize are both major food crops grown in dry parts of the world, yet sorghum can give higher yields than maize when water is very scarce. One reason is that sorghum plants have a smaller leaf area than maize, and another is that sorghum leaves contain rows of motor cells along the midrib on the upper side of the leaf, which enables the leaves to roll up.

May/June 2011

Section B. Answer just one question.

May/June 2017

The structures, processes and compounds that are involved in photosynthesis in C4 plants include: A - carbon dioxide B - phosphorylation C - palisade cells D - PEP carboxylase E - rubisco F - malate G - RuBP H - mesophyll cells I - guard cells J - photorespiration K - photolysis L - oxaloacetate M - ATP synthase N - chlorophyll

May/June 2020

In plants, stomata open or shut as environmental conditions vary.

May/June 2024

Guard cells sit in the epidermis of most plant leaves. When environmental conditions alter, the guard cells change in ways that regulate whether stomata are open or closed.

May/June 2025

The grass Oryza sativa is cultivated as a food crop for rice production. Rice plants are adapted to live with their roots submerged in water. An experiment was done to study the formation of aerenchyma tissue in the roots of rice plants. - 10-day old seedlings were grown with their roots submerged in water. - Some were grown in water that was kept oxygenated, while others were grown in water that had no oxygen (deoxygenated). - At 12 hour intervals, some seedlings from each group were taken out and transverse sections of their roots were prepared and examined. - The sections were cut at the same distances from the root tip to assess development. - The percentage of root tissue that had developed into aerenchyma tissue was calculated. The results are shown in Fig. 7.1.

May/June 2025

Fig. 1.1 depicts part of a guard cell.

Oct/Nov 2019

If the water supply to a plant falls, the concentration of abscisic acid (ABA) in the leaves rises. ABA attaches to receptors in the cell surface membranes of guard cells. This starts a sequence of events inside the cells, leading to stomatal closure. Fig. 8.1 is a diagram of part of a guard cell showing some of the events that take place when ABA attaches to its receptor. Fig. 8.1 indicates that calcium ions take part in the events within a guard cell that lead to stomatal closure.

Oct/Nov 2025