Plant responses - spec

Give examples of abiotic stress that plants respond to

Temperature, salinity, nutrient deficiency, drought/flooding

How do plants prevent freezing after long periods of low light?

Actively transport salt into their vacuole and cytoplasm, lowering the freezing point, so water will not expand as it freezes

How do clinostats work?

Stimulate a weightless environment by cancelling out Earth’s gravity on plant growth - equal gravity on all sides means the plant grows horizontally straight out

Define herbivory

Feeding on plants

What are the defences plants use in response to herbivory?

Alkaloids, pheromones and folding in response to touch

Describe the role of alkaloids

Bitter tasting nitrogenous compounds that poison insects that ingest them

Describe the role of pheromones

Chemicals which affect the social behaviour of the same species

Define tropism

A directional growth in response a stimulus

Define thigmotropism

Directional growth in response to a touch stimulus

Define chemotropism

Directional growth in response to a chemical stimulus

Define nastic response

A non-directional growth

What is the meristem in plants?

Regions of unspecialised cells

What is the apex of a plant?

The highest point/tip of plant

Define phototropism

A directional growth towards a light stimulus

Define geotropism

A directional growth towards gravity

How can you investigate geotropism in plant?

Using a clinostat - constantly spinning a plant - ensures gravity is acting on all sides equally

Describe the role of auxin in leaf loss in deciduous plants

Inhibits leaf loss (produced by young leaves)

Describe the role of ethene

Stimulates leaf loss, promotes fruit ripening

Describe the mechanism of action of ethene promoting leaf loss

Causes formation of abscission layer by causing cells to explains and cell walls to break, making them rupture

Form a protective layer to prevent entry of pathogens into cytoplasm

Describe the role of gibberellins

Stimulates seed germination and flowering

Describe the role of abscisic acid

Stomatal closure

Describe the role of cytokinins

Cell division/differentiation

Describe the action of auxin when light hits one side of a plant

Auxins accumulate on shaded side of shoot and cause cell elongation so bright side bends towards light

Describe the action of auxin when a plant is in soil (geotropism)

Auxins accumulate at bottom of root due to gravity and inhibit growth of root cells, so opposite side continues to grow and elongate

How does auxin bring about apical dominance?

High concentrations of auxin suppress lateral growth

How do shoots further down the plant continue to grow despite auxin being present?

Auxin concentration decrease down the plant so lateral buds can grow wider further away from apex

Why is auxin concentration decreasing down the plant a benefit for plants?

Shoots at top of plant will grow vertically not laterally, allowing light to reach leaves on wider-growing shoots further down

How does gibberellin control seed germination?

Gibberellin stimulates breakdown of starch into glucose inside the seed, which the embryo can use for respiration to grow

How does gibberellin concentration affect stem elongation?

Promotes stem elongation by stimulating cell division within stem

Which hormone controls ripening in fruit industry?

Ethene

Which hormone is used as a rooting powder to stimulate growth on plant cuttings?

Auxins

Which hormone is used as a hormonal weed killer?

Auxins

How do hormones act as hormonal weed killers/herbicides?

Stimulate cell elongation so that stem of weed grows so fast that it can’t sustain itself and dies