Plant Responses OCR A level Biology

What does abiotic mean?

Non-living

What does biotic mean?

living

What is the definition of tropism?

Growth response to a stimulus

What are some examples of an abiotic stimuli?

Light, water, gravity

What are some examples of biotic stimuli?

touch, chemicals

What is phototropism?

A plant's response to light

What is geotropism?

a plant's response to gravity

What is hydrotropism?

A plant's response to water/moisture

What is thigmotropism?

a plant's response to touch

What is chemotropism?

growth in response to chemicals

What is photoperiodism?

A plant's response to seasonal changes in length of night and day

What is nastic movement?

a non-directional responses which is not related in any way to the direction of the stimulus

What is an example of a plant that presents nastic movement?

Mimosa Pudica

What happened to the Mimosa Pudica plant in response to touch?

the leaves fold in very rapidly

What are tannins made from?

water-soluble carbon compounds

What is the name is of the group that tannins belong to?

flavonoids

Where are tannins stored in the plant?

In the vacuole

What is the toxic affect of tannins a result of?

the breakdown of tannins which produces toxic chemicals

How does a plant use tannins to promote survival?

They have a bitter taste, and can be fatal to insects so will reduce herbivore populations

What are alkaloids composed of?

Nitrogenous compounds derived from amino acids

How are Tannins and alkaloids similar?

both have a bitter taste and can be toxic

what are some examples of alkaloids?

Caffeine, nicotine, capsaicin

What are pheromones?

chemicals that are released by a member of a species that affect the physiology or behaviour of another member of the same species

What is an example of a pheromone?

ethene

What does ethene do to plants?

stimulates the ripening of fruit

Causes leaf loss

causes physiological changes

oxidides of ethene are toxic to insects

How do plants respond to droughts?

closing stomata

loosing leaves

How do some plants respond to cold?

certain plants produce chemicals which act as an anti-freeze and prevents the formation of ice crystals

In terms of phototropism, how are shoots described?

positively phototropic

Why are shoots positively phototropic

they grow towards the light which ensure maximum leaf area for photosynthesis

What is abscisic acid (ABA)?

Plant hormone that inhibits seed germination and growth, and causes stomatal closure when water is limited

What is the definition of abscission?

the shedding of leaves

What is apical dominance?

Suppression of growth of lateral buds caused by hormones produced by the apical bud.

What is phototropism coordinated by?

indole-3-acetic acid (IAA)

Where is IAA synthesised?

in the meristem and passes down the stem to stimulate extension growth

What is though to be the result of negative geotropism of plant stems?

accumulation of auxin

What are gibberellins?

plant hormones that promote stem elongation, seed germination and cell division

What is leaf loss caused by?

the development of a layer of cells called the abscission layer

What does the plant hormone ethene stimulate?

the breakdown of cell walls in the abscission layer

How do auxins inhibit leaf loss?

they make the leaf stalks insensitive to ethene

What happens to the concentration of auxins as the plant gets older?

the concentration of auxin decreases and this allows leaf loss to occur in response to ethene

Where is abscisic acid (ABA) formed?

in the roots of the plants in response to decreased soil water potential

Describe the process of stomatal closure

- ABA binds to receptors on the cell surface membrane of guard cells

- A complex series of events is set in motion which results in the opening of calcium channels causing ca2+ ions to enter

- the PH of the cytoplasm is also raised

-These events cause potassium ions and also nitrate and chloride ions to leave the cell

-As a result the water potential of the cell increases and water is moved by osmosis into surrounding cells

- this results in the stomata to close

Describe the process of the leaf falling

- As the leaves age, rate of auxin production declines.

- Leaf is more sensitive to ethene production

more ethene produced, inhibits auxin production

- Abscission layer to grow at the base of the leaf stalk

- leaf fall

What are the three most important hormones jin germination?

Gibberellins, abscisic acid and auxins

What experiment showed that gibberellins stimulate germination?

Mutant strains of the plant arabidopsis that originally produce no gibberellins but can be induced to germinate if gibberellins are applied.

How do gibberellins stimulate seed germination?

Gibberellins released by the embryo travel jot the aleurone layer, a layer of cells surrounding the endosperm of the seed. Gibberellins cause the aleurone layer to produce amylase, which breaks down starch stored in the endosperm into sugar, providing energy for the growth of the embryo and breaking dormancy

How does abscisic acid help to maintain dormancy?

by inhibiting the production of amylase

What is the germination process dependant on?

auxin concentration

What is the commercial use of auxins?

-selective weed killlers

- lower doses auxins are used to stimulate root growth in cuttings

- auxins can be sprayed on fruit to prevent fruit drop

What is the commercial use of ethene?

-stimulates the ripening of fruit

What is the commercial use of auxins and gibberellins together?

to treat unpollinated flowers

What is the commercial use of cytokines?

delay raging of leaves