Pop-Quiz

•Define a negative feedback system

•Which organ produces the hormones that are used in regulation of blood glucose?

•Define Homeostasis?

answer

•A negative feedback system involves an original stimulus and the body reacting to return that stimulus back to a normal level•Regulation of blood glucose involves two hormones produced by the pancreas

Plant

Responses

and

Adaptations

Hormone-producing

cells

Target cells

Movement of hormone

Hormone Action on Plants

A. Plant cells can produce hormones: which are chemical messengers that travel throughout the plant causing other cells called target cells to respond.

B. In plants, hormones control:

1. Plant growth & development

2. Plant responses to environment

Cells in one blooming flower signals other

blooms using hormones to open.

Plant Hormones

Hormones in plants are responsible for:

Phototropism

Geotropism

Apical dominance

Ripening of fruit

abscission

Plants are also in an environment that is constantly changing.

They need to have a way to do this. Even though they do not have a nervous system plants do have hormones.

Plant cells will send signals to one another to tell them:

1.When trees to drop their leaves.

2.When to start new growth.

3.When to cause fruit to ripen.

4.When to cause flowers to bloom.

5.When to cause seeds to sprout.Leaf Drop

Fruit Ripening

Sprouting Corn Seeds

Cactus Blooming

Tree Budding

Plant hormones

The main groups of plant hormones are:

Auxins

Gibberellins

Cytokinins

Abscisic acid

ethylene

Auxins

Auxins promote growth of new shoots, trigger positive phototropism and negative geotropism of shoots and are responsible for apical dominance (inhibition of growth of lower branches)

Eg Indoleacetic Acid (IAA), it is responsible for Geotrophism

Gibberellins

Gibberellins (GAs) are plant hormones that regulate growth and influence various developmental processes, including stem elongation, Initiates seed germination, dormancy, flowering, sex expression, and leaf and fruit senescence.

Cytokinins

Cytokinins work in conjunction with Auxins to stimulate cell division and differentiation (cell reproduction).

Cytokinins are synthesised in stems, leaves and roots

Abscisic acid

Growth inhibiting hormone with actions opposite to those of auxins. Its roles include abscission of flowers fruits and leaves and control of stomatal movement.

Inhibits growth

Abscisic acid suppresses cell growth. It also promotes leaf senescence (towards death) which results in the colour changes of leaves in autumn before they are dropped from deciduous plants.

Ethylene causes Fruit to Ripen

1.Fruit tissues release a small amount of ethylene

2.Causes fruits to ripen.

3.As fruit become ripe, they produce more and more ethylene, accelerating the ripening process.

Ethylene released by apples and

tomatoes causes fruit to age quickly.

Plants responding to external environments

Plants do not monitor internal environment but are sensitive to environmental stimuli such as:

Light, gravity, temperature, touch, water, carbon dioxide.

We have seen how they respond to these stimulus using hormones.

summary

Hormones in plants are responsible for phototropism, geotropism, apical dominance, ripening of fruit, abscission.The main groups of hormones are Auxins, gibberellins, cytokinins, abscisic acid and Ethylene