plant responses

Question 1

A student setting up an experiment to investigate the effect of light on cress plant seedlings accidentally shone the bright light onto one side of the face of another student. He noticed that the student immediately responded by raising her hand to shield her eye from the light. The response of the cress seedlings to light shining from one direction was slower, but after 24 hours the cress seedlings had grown towards the light.
Describe the mechanisms that produced the responses to light in the cress seedlings and in the human.

Answer 1

cress seedlings
C1 apical cells / apex/ tip(of shoot), produce , auxin /
IAA ;
C2 diffusion / active transport
(down shoot / through parenchyma) ;
C3 greater auxin (concentration)
on shaded side of stem ;
C4 auxin causes cell wall loosening ;
C5 auxin causes cell , elongation / expansion ;
C6 further detail of changes in cell wall ;
Human
H1 retina / rods / receptors, detect light / AW ;
H2 action potentials/ depolarisation/nervous impulse,
along sensory neurone (membrane) ;
H3 intermediate neurone (in brain) /
(somatic) motor neurone /
neuromuscular junction ;
H4 correct ref to detail of synaptic transmission;
H5 depolarisation / contraction, of muscle fibre(s);
H6 correct ref to detail of muscle contraction;

Question 2

Rhubarb leaves contain oxalic acid, a relatively strong acid which is soluble in water and alcohol. High concentrations of oxalic acid makes rhubarb leaves poisonous to humans and other animals. (i) The amount of oxalic acid in the leaves varies according to the variety of rhubarb, the age of the plant and environmental factors.Suggest and plan an experiment to compare how the variety of rhubarb affects the amount of oxalic acid in rhubarb leaves.Include in your plan:
• the variables that you could control
• an outline of the experimental procedure you would use
• any measurements that you would make.

Answer 2

1 (test) different varieties ;
2 several plants or leaves (of each) /
repeat readings ;
3 same age ;
4 same soil , type / mineral content / pH ;
5 same light , exposure / conditions ;
6 same , watering regime / temperature /
 CO2 concentration ; 
7 same, preparation or testing procedure detail ;
 (e.g. leaf mass / volume of solvent /
 soaking time / temperature)
8 test / measure, (oxalic) acid concentration /
 acidity / pH / H+ ion concentration ;
9 detail of measuring method ;

Question 3

Use your knowledge of plant growth regulators (plant hormones) to suggest why shoots kept in the dark grow taller than those left in the light.

Answer 3

auxin / IAA ;
not destroyed by light / more present in dark ;
moves down from shoot tip / uniformly distributed ;
(causes) cell elongation ;

Question 4

Describe two ways in which hormones may alter a plant’s growth in response to overcrowding by other plants.

Answer 4

auxin / IAA ;
(positive) phototropism ;
plants / shoots, bend towards light ;
etiolation / plants grow taller ;
climbing plants climb, up / over, other plants ;
(positive) thigmotropism / sense of touch ;
grow roots towards, water / minerals ;
allelopathy / description ;

Question 5

Suggest how hormones alter a plant’s growth if the top of the plant shoot is eaten by an animal.

Answer 5

less auxin / auxin production stopped ;
apical dominance, stopped / removed ;
side shoots grow / lateral buds develop / ora ;
plant becomes bushy ;

Question 6

plants that lose their leaves seasonally

Answer 6

deciduous ;

Question 7

Explain why plants need to be able to respond to their environment.

Answer 7

Explain why plants need to be able to respond to their environment.

Question 8

State two commercial uses of plant growth substances.

Answer 8

seedless, fruits / grapes ;
weedkillers ;
rooting powder / to grow cuttings / used in tissue culture ;
control fruit ripening ;
controls fruit drop ;
restrict hedge growth ;
preserve, cut flowers / green vegetables ;
specific example of improved fruit quality ;
producing malt / in brewing ;