plant responses

What name is given to the growth response of plants to light?

phototropism

How does phototropism benefit plants?

• it can receive the maximum amount of light

• maximum photosynthesis

Name the types of growth response in plants.

• phototropism-growth response of a stem towards light.

• geotropism-the growth of a plant in response to gravity—it

  Roots are positively geotropic and shoots are negatively geotropic.

• chemotropism-the response to chemicals, e.g. pollen tubes
  growing down the carpel in response to chemicals released
  by the ovule.

• thigmotropism-the growth of a plant in response to contact (Touch)
  e.g. vines wrap around objects which help support the plant.

• hydrotropism-the response of roots to water – they will grow towards it. 

  
  

plant growth regulator.

a chemical (hormone) that controls growth.

it can promote or inhibit growth

Describe the mechanism of any one plant growth response to an external stimulus.

phototropism

• auxin ( growth regulator) is produced in the meristem of shoot tip

• auxin diffuses down the shaded side of the stem ( vascular tissue)

• this causes an unequal distribution of the auxin

• the side with the higher auxin grows more quickly

• this causes the plant to bend towards the light

Give one example of the use of plant growth regulators, e.g. by horticulturists.

• seedless fruits

• rooting powder

• herbicide

• tissue culture

Plants have adaptations that help in protection. Give any two methods plants use to protect themselves.

• thorns-prevent plants from being eaten

• stinging cells in epidermis prevent plants being eaten

• production of tannins make the plant indigestible

• production of nicotine in legumes that damage nerves and muscles

• cyanide production in cherry pits

Answer the following based on investigating the effect of IAA on plant tissue.

1. Name a suitable plant tissue you used.

2. Describe how you measured the effect of IAA on plant tissue.

radish seeds

used a ruler to measure the length of shoots and roots

Name the substance that causes the change in mass of the plant tissue.

water

What term is given to the movement in and out of the plant tissue of water

osmosis

What term is used to describe the condition of the plant cells that have been soaked in the 0 g/100 cm3 sugar solution?

turgid

Explain how plant cells maintain turgidity

presence of the cell wall and vacuole

Explain in detail why the mass of the plant cells reduces in the 12 g/100 cm3 sugar solution.

• water has moved out of the cells by osmosis

• water moves from an area of high water concentration to an area of low water concentration across a semi-permeable membrane

What do you think would happen to an animal cell in the 0 g/100 cm3 sugar solution?

swell/burst

State a location in plants where growth regulators are produced.

meristem

How are growth regulators transported around a plant?

transported in the xylem and phloem - vascular tissue

Describe how you set up the investigation on the effect of IAA growth regulator on a plant tissue

• label 8 petri dishes 1 to 8

• fit a circular acetate grid in the base of each dish and place 6 radish seeds across the middle on a grid line

• add a layer of Vaseline

• place some cotton wool over each filter paper and pour the remaining 6 ml of each solution onto the cotton wool

• fit the lids and seal the petri dishes with tape

• stand the petri dishes on their edge and leave in an incubator at 25C for 3 days

Describe any one result of your investigationof IAA experiment

• at high concnetrations, the shoot elongates

• at low cicnentrations the root elogates

describe one safety precaution you took in carrying out this investigation of IAA experiment

• use gloves

• lab coat

tropism

the growth response of a plant to a stimulus

germination

the re-growth of a seed after a period of dormancy if the environmental conditions are suitable to form a new plant

dispersal

The carrying of a seed/fruit away from the parent plant.

dormancy

a resting period when seeds undergo no growth and have reduced cell activity or metabolism

how does dormancy in seeds benefit plant species

• plants avoid harsh winter conditions

• gives the embryo time to develop

• provides time for successful dispersal

2 roles of water in process of germination

• activates the enzymes

• medium for germination reactions - digestion

• transport medium for digested products

2 possible food stores in seeds

cotyledon

endosperm

3 factors necessary for germination

• water

• oxygen

• suitable temperature

Answer the following questions in relation to an investigation you carried out to show digestive activity during seed germination.       

State whether your used starch agar or skimmed milk (protein) agar. 

starch agar

Why were the seeds soaked in water prior to the investigation? 

to activate the digestive enzymes and soften the testa

Describe how you further prepared the seeds and added them to the agar plate(s).  

• soaked the seeds in bleach for 5 mins to sterilise them so they don’t rot

• cut each seed lengthways

• place each half onto the starch agar, cut surface down

Under what conditions did you store the plate(s) containing the seeds to allow  germination to occur? 

incubate the dish at 20C for 5-7 days

How did you test to show that digestion had occurred? 

• flood the plate the iodine

State the result that showed digestion had occurred.

• starch agar with boiled seeds ( control) had turned blue-black as the starch had not been broken down

• starch agar with unboiled seeds remained yellow/brown under where the seeds had been, zones of clearing

Where precisely in plants are auxins produced? 

meristem

state why the action of an auxin is considered to be similar to the action of a hormone in the human body

• both are chemical in nature

• both made in one location and act in another

• both transported by vascular tissue

• their effects are widespread and have a prolonged effect

auxin

a plant growth regulator

example of an inhibitory function of auxin

apical dominance

exactly how does an unequal concentration of auxin in the elongation zone affect the growth of a shoot and a root

• shoot-higher auxin concentration results in higher rate of cell division

• root-higher auxin concentration results on lower rate of cell division

suggest what would cause an unequal concentration of auxin in a shoot and a root

• shoot-difference in light direction

• root-gravity/difference in water concentration

reasons why dispersal is important to plants

• minimises competition

• avoids overcrowding

• colonises new areas

• increases chances of survival

way in which knowledge of seed dormancy is useful to humans

• optimum sowing time

• maximise growing season

What is the role of digestion and the role of respiration in seed germination? 

digestion-provides soluble nutrients

respiration-provides energy for growth and embryo

The graph below shows variations in the dry mass of peas over a period of time after germination. Give a reason for:  

1.The initial decrease in mass          

2. The subsequent increase in mass.    

• respiration

• photosynthesis

Place the letter X on your diagram, to show the part of the leaf in which most photosynthesis occurs and explain why it occurs mostly there. 

palisade layer

• close to sunlight

• more chloroplasts

State two other ways in which the leaf is well adapted for photo synthesis.

• flat and thin

• air spaces

• large number of stomata and chloroplasts

• vascular system

 Name three substances which are involved in leaf metabolism and which pass  through the stomata. 

• carbon dioxide

• oxygen

• water

The concentration of which gas influences the diameter of the stomata?

carbon dioxide

Name a type of enzyme in the seed that carries out this digestion.

amylase

When preparing the seeds, they were also split and sterilised.

Why were the split seeds placed open-side down on the agar?

to ensure there is good contact of the enzyme amylase with the substrate starch

What name is given to the regions of plants which secrete growth regulators?

apical meristems

Give an example of a growth regulator which has a negative effect on plant growth.

IAA

thigmotropism.

the growth if a plant in response to contact e.g vines wrap around objects which help support the plant

Following fertilisation, from precisely which part of the flower is the seed formed?

ovule

What is meant by the term monocotyledonous?

one seed leaf

Name two biomolecules stored in endosperm or cotyledon tissue.

lipids

protein

carbohydrate

At the start of the investigation to show digestive activity during germination the seeds were sterilised. 1. Why is this necessary?

• to kill any micro-organisms

Name the substance that is used as a medium on which to germinate the seeds.

starch agar

What substance, to be digested by the seeds, was added to the above medium?

starch

What control did you use in this demonstration?

boiled seeds for 10 mins

Name a plant growth regulator that promotes growth and give a precise location for a site of its action.

auxin (IAA)- meristem

through which part of a stem are growth promoters transported?

vascular tissue

Give an example of a growth regulator that inhibits growth.

auxin

adverse external environment

surroudings that are harmful to organisms

Name the group of substances in plants which control responses to external stimuli.

plant growth regulators

What name is given to the regions in plants in which these substances are produced?

Give locations for two of these regions.

meristems

root tip/bud

positively phototropic.

growth repsonse of a stem towards light

Water, oxygen and a suitable temperature are all required for the germination of seeds. In the case of each of these factors describe its effect on the process of germination.

water

• activates enzymes

• medium for reactions(digestion)

• transport mediums for digested products

oxygen

• needed for aerobic respiration

suitable temperature

• allows maximum enzyme activity

Which part of the embryo in a germinating seed gives rise to each of the following parts of the seedling?

• The root

• The shoot.

• radicle

• plumule