Survival and response

Define taxis

Directional response to a stimulus

Organism moves the whole body to or from a favourable stimulus 

Define kinesis

Non directional response to a stimulus

Organism changes the speed of movement and the rate it changes direction 

What is a tropism

A growth movement in response to a stimulus

What is IAA

Indoleacetic acid 

Growth factor

Type of auxin 

What effect does IAA have on root cells

It inhibits growth and elongation 

What effect does IAA have on shoot cells

Stimulates cell growth and elongation

Describe gravitropism in roots of plants

• IAA difffuses downward toward gravity 

• Roots grow toward gravity

• Cells in upper surface will grow amd elongate whereas cells in lower surface will be inhibited

• Positive gravitropsim-toward stimulus 

Describe phototropism in roots of plants

• IAA diffuses away from light 

• Roots grow away from light

• Cells nearer to the light will grow and elongate more than cells nearer to the dark

• Cells nearer to the dark will be inhibited

• Negative phototropism 

Describe phototropsim in shoots of plants 

• IAA diffuses away from the light

• Shoots grow towards the light

• Shaded side has more IAA so cells there grow and elongate more

• Positive phototropism

Describe gravitropism in shoots of plants

• IAA diffuses toward gravity Roots grow

• Shoots grow away from gravity 

• Lower side has more IAA so cells there will grow and elongate more whereas the cells in the upper side of shoot have less IAA so do not grow and elongate more

• Negative gravitropism-away from stimulus 

How would an animal which uses taxis respond to an unfavourable stimulus 

Move directly away from stimulus -straight line 

How would an animal which uses taxis respond to a favourite stimulus

It would move directly toward the stimulus

Straight line 

How would an animal which uses kinesis respond to an unfavourable stimulus

Have a lower rate of turning higher rate of movement 

Help to get out of the area and move to different conditions 

How would an animal which uses kinesis respond to experiencing a favourable stimulus 

Have a higher rate of turning and a lower rate of movement Help to

Help animal stay in the same area

Suggest one advantage of the behaviour shown and name type of behaviour

-moving toward light source

Taxis

Less competition for light

Find mate

Explain why the student removed the shoot tip from each seedling when determining how IAA conc impacts shoots

IAA is produced in shoot tip

Would affect the concentration IAA

Mitosis occurs in shoot tips

Affects length/growth

Explain why the student added glucose solution to each Petri dish

Glucose needed for respiration to make ATP

Explain why the lids were kept on Petri dishes

Prevent evaporation of IAA

also concentration does not change

Describe and explain results in table 1 suggest how results might have differed if lengths of root had been used

+ve correlation

As IAA conc increases mean change in lentgh of shoot also increases because IAA diffuses into shoot

Promotes cell growth and elongation so shoots with higher IAA conc grow faster

Roots change in lentgh decrease IAA inhibits cell growth in roots