Survival and response (A-level only) Flashcards – AQA A-Level Biology - (7402)

What is indoleacetic acid (IAA), and what aspect of plant growth does it affect?

IAA is a plant growth factor that affects cell elongation.

Where is IAA produced, and where is it transported?

It is produced in growing regions and transported to other tissues.

What two factors determine IAA’s effect on cell elongation?

Its concentration and the tissue responding.

How do roots and shoots differ in their sensitivity to IAA?

Roots are more sensitive: an IAA concentration that promotes shoot cell elongation can inhibit root cell elongation.

How can differences in IAA concentration across a growing organ cause it to bend?

They cause unequal growth across the organ, producing bending.

What is phototropism?

A directional growth response to light.

How is IAA distributed in a shoot illuminated from one side?

More IAA accumulates on the shaded side.

How does higher IAA on the shaded side affect a shoot’s growth?

It promotes greater cell elongation there, bending the shoot towards the light. This is positive phototropism.

What is negative phototropism in roots?

Growth away from light.

How can an uneven IAA distribution cause a root to bend away from light?

Greater IAA on the shaded side inhibits elongation there relative to the illuminated side, bending the root away from light.

What is gravitropism?

A directional growth response to gravity.

How is IAA distributed when a root or shoot is placed horizontally?

IAA becomes more concentrated on the lower side.

How does IAA cause a horizontal shoot to show negative gravitropism?

IAA promotes greater elongation on the lower side, bending the shoot upwards, away from gravity.

How does IAA cause a horizontal root to show positive gravitropism?

IAA inhibits elongation on the lower side relative to the upper side, bending the root downwards, towards gravity.

What is a taxis?

A directional movement response by a mobile organism to a directional stimulus.

How do positive and negative taxis differ?

In positive taxis, the organism moves towards the stimulus; in negative taxis, it moves away.

How can taxis help an organism survive?

It can direct movement towards favourable conditions or away from unfavourable ones, helping the organism remain in a suitable environment.

What is kinesis?

A change in a mobile organism’s movement activity in response to stimulus intensity, rather than movement towards or away from the stimulus.

Which two aspects of movement may change during kinesis?

Movement speed or turning rate.

How can kinesis make an organism more likely to remain in a favourable environment?

The organism moves more and spends less time in unfavourable conditions, but moves less in favourable conditions.

What is a simple reflex?

A rapid, automatic response to a stimulus that does not require a conscious decision.

What protective role can a simple reflex serve?

It can protect an organism from harm.

What is the sequence of events in a three-neurone reflex arc?

1. A receptor detects a stimulus.
2. A sensory neurone carries an impulse to the central nervous system.
3. The sensory neurone communicates with a relay neurone, then a motor neurone.
4. The motor neurone carries an impulse to an effector, which produces the response.

What are the connections between neurones in a reflex arc called?

Synapses.

What two types of apparatus can be used to investigate an animal’s movement response to an environmental variable?

A choice chamber or a maze.

How should conditions be arranged to investigate an animal’s response to one environmental variable?

Vary the variable between regions or trials, while controlling other relevant conditions as far as possible.

How can movement or distribution be recorded in an animal movement investigation?

Record it consistently, for example by counting animals in different regions or measuring movement over a set time.

Why should observations or trials in an animal movement investigation be repeated?

To assess patterns and variation.

What can a difference in animal distribution alone not establish about the movement response?

Whether it was caused by directional movement or a change in movement activity.

What animal welfare precautions should be taken when investigating movement?

Handle animals appropriately and expose them to conditions that avoid unnecessary harm.