Growth Response in Plants

8/4/2019 Growth Response in Plants

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2/31

A directional growth movement

made by a part of a stationary

plant response to unilateral

stimulus


3/31

Types of Tropism

shoot

root

hydrotropism

no response

positive

geotropism

negative

positive

stimulus

tropism

response

watergravity unilateral light

phototropism

positive

negative


4/31

Importance of Geotropism

provide firm anchorage for roots ensure the plant can get

adequate supply of water &

mineral salts


5/31

To show Geotropism

in Seedlings


6/31

What has happened to the radicles and plumules ?Ans: The radicles grow downwards, while the plumules

grow upwards.

in complete darkness in complete darkness

P

Q R

P

Q R

plumule radicle

after 2 days

(a) Beginning of experiment (b) End of experiment


7/31

Why is it necessary to leave the apparatus in darkness ?

Ans: To avoid any stimulus from light.


P

Q R

P

Q R

plumule radicle

after 2 days



8/31

Do the radicles show positive geotropism or negativegeotropism ?

Ans: Positive geotropism.


P

Q R

P

Q R

plumule radicle

after 2 days



9/31

What advantage do the seedlings have by showing suchgeotropism ?

Ans: Roots grow downwards deep into the soil to provide

a firm anchorage underground and absorb water and

mineral salts in the soil.


P

Q R

P

Q R

plumule radicle

after 2 days



10/31

Clinostat

for control experiments

contains a cork disc which can be set to rotate

in a vertical or horizontal plane by a motor to make factors uniform (evenly distributed)


11/31

To show the effect of

Gravity by using a Clinostat


12/31

What is the purpose of marking the radicles at equalintervals ?

Ans: To find out which region of the radicle grows faster.

plastic cover lined with

moist blotting paper

X

Y

in complete

darkness

seedling in X

seedling in Y


13/31

Does the direction of growth of the seedlings inclinostats X and Y change ?

Ans: The radicle of the seedlings in clinostat X bends

downwards in response to the pull of gravity



X

Y

in complete

darkness

seedling in X

seedling in Y


14/31

Does the direction of growth of the seedlings inclinostats X and Y change ?

Ans: since every side of the radicle of the seedling in

clinostat Y is acted on by gravity, the radicle will

grow straight horizontally.



X

Y

in complete

darkness

seedling in X

seedling in Y


15/31

What is the purpose of setting up clinostat Y ?Ans: Serve as a control for comparison.



X

Y

in complete

darkness

seedling in X

seedling in Y


16/31

Importance of Phototropism

enables leaves to be in a positionto receive as much sunlight as

possible for photosynthesis


17/31

To show Phototropism

in Shoots


18/31

What has happened to the shoots of plants A, B and C ?

Ans: The shoots in pot A respond by growing towards the

light source. The shoot in pot B do not show any

curvature but grow vertically upwards...

unilateral

light

unilateral

light

in complete darkness

A B C

light-proof

box clinostat


19/31

What has happened to the shoots of plants A, B and C ?

Ans: the shoots in pot C grow vertically upwards with

slender and longer nodes, and carries smaller leaves

which are yellow in colour.

unilateral

light

unilateral

light


A B C

light-proof

box clinostat


20/31

What is the effect of the clinostat on the shoot of plant B ?

Ans: The revolving clinostat cancel out the effect of

unilateral light on the shoot of plant B.

unilateral

light

unilateral

light


A B C

light-proof

box clinostat


21/31

What is the significance of phototropism to plants ?

Ans: This tropism ensures that a plant gets enough light

energy for photosynthesis.

unilateral

light

unilateral

light


A B C

light-proof

box clinostat


22/31

Importance of Hydrotropism

ensures that a plant gets enoughwater as a raw material for

photosynthesis & enough mineral

salts to maintain normal growth


23/31

no growth grows

dark box

few days later

Conclusions :

The tip is responsible for growth

cut & replaced tip

decapitated

Experiments

on Oat Coleoptiles


24/31

unilateral

light

few days later

black covers

Conclusion :

the tip is the place responsible for bending

Experiments

on Oat Coleoptiles


25/31

Experiments

on Oat Coleoptiles

fewdayslater

dark box

agar plate

Conclusions :

the head must have produced a diffusible

chemical substance which stimulates growth


26/31

Experiments

on Oat Coleoptilesbending directions

Explanation of results :

The side with the tip has a higher concentration of that particular

chemical, the growth rate is faster than the other side

the tip is put aside

bending directions

mica

plate

Can the explanation still work ?


27/31

Auxins

commonest plant hormones

regulate growth & other physiologicalprocesses in plants

produced by root tip / shoot tip

they affect the elongation region of the

tip


28/31

Effect on Plant Parts

positivegrowth

negative

growth root

shoot

auxin

concentration

Growth of

plant

high conc. low conc.

auxin concentrationplant growth

shoot

root

positive no effect

negative positive

high

conc.low

conc.


29/31

Phototropism in Shoot

The shoot tip produces auxins which diffuse downward

The auxins diffuse to the shaded side due to the presence

of unilateral light

High auxin concentration

stimulates growth in shoot

The shaded side grows faster

than the lighted side

The shoot bends towards the light


30/31

Geotropism in Root The root tip produces auxins which diffuse to the

elongation region

The auxins diffuse to the lower side due to gravity

High auxin concentration inhibits growth in root

The lower side grows slower than the upper side

The root bends downward


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~END~

Growth Response in Plants

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