Unit 6 - Organisms respond to changes in their environment

what is the sequence of events in a response to a stimulus?

stimulus - detectable change in the internal or external environment of an organism

receptor - detects specific types of stimulus

coordinator - coordinates a suitable response to a stimulus

effector - produces a response to a stimulus

response - the action

what is a taxis?

a simple response whose direction is determined by the direction of the stimulus

what is the difference between positive phototaxis and negative phototaxis?

positive is when the organism moves towards light

negative is when the organism moves away from light 

what is a positive chemotaxis?

is when an organism moves towards a region where a specific chemical is more concentrated 

what is a kinesis and how does it help increase the chance of survival in some organisms?

a kinesis is a response in which the organism changes the speed at which it moves and the rate at which it changes direction, it can increase an organism’s chances of survival by enhancing its chances of a quick return to a favourable environment

what is tropism?

is the growth of a part of an organisms like a plant in response to a directional stimulus

what are positive phototropism and negative phototropism and how are they helpful to plants?

positive phototropism is when the part of the plant grows towards light this increase the probability that leaves will be able to capture light

negative phototropism is when a part of an organism grows away from light this increases the probability that the plant roots will grow into the soil where they can absorb more water and mineral ions

what are the three main stimuli most plants respond to?

light, gravity and water

what is positive hydrotropism in plants and why is this beneficial for their survival?

it is when plant roots grow towards water, it allows the roots to absorb more water which is essential for transport and photosynthesis

what is indoleacetic acid?

IAA is a plant growth factor that controls plant cell elongation it is a type of auxin

how does IAA control positive phototropism in shoots?

IAA is produced in cells in the tip of the plant shoot

IAA is transported down the plant shoot

light stimulates IAA to move from the light side of the shoot to the shaded side 

IAA becomes concentrated and stimulates more cells elongation on the shaded side of the shoot 

meaning the shoot bends towards the light 

how does IAA control negative phototropism in roots?

IAA is produced in cells in the tip of the plant root

IAA is transported along the plant root

light stimulates IAA to move from the light side to the shaded side 

IAA becomes concentrated and inhibits cell elongation in the shaded side 

meaning the root bends away from light 

how does IAA control positive gravitropism in roots?

IAA is produced in cells in the tip of the plant root

IAA is transported along the plant root 

gravity moves IAA from the upper side of the root to the lower side of the root

IAA becomes concentrated and inhibits cell elongation in the lower side of the root 

the root bends downwards towards the force of gravity

what are plant growth factors and how are they different from animal hormones?

they are chemicals produced in plants that influence their growth and development

how does auxin control growth by elongation?

auxin binds to cell surface membrane 

hydrogen ions are actively transported from the cytoplasm into the cell wall

the cell wall becomes more plastic 

cells elongate and plant grows