G 1 - Plant responses to the enviroment

How do shoots respond to light?

Auxin's are light sensitive hormones that move away from the light source. As a result the cells on the dark side of the plant ( the side not recieving light attention) elongates and the light side bends towards the light stimulus (cells do not elongate on this side).

what Pathogens damage a plant?

Bacteria Fungi

Why does the plant respond to gravity in this way?

Because the Auxin's accumulate on the LOWER SIDE of the shoot and root due to the influence of gravity 1. As a result of this high concentration of Auxin's in the LOWER SIDE of the shoot, it begins to grow in an upward curvature. I.e the main stem is negatively geotropic. 2.In the root the high concentration of auxin's stops further growth on the LOWER SIDE. Cells on top of the root are not affected by the concentration of auxin's and as a result cause cell elongation which makes the root grow downwards. I.e the main root is positively geotropic.

What does Dicotyledons mean?

Broad Leaf

What does Abscission mean?

Cutting Off.

How can Weed Control damage the earth?

If done Mechanically it can damage the soil structure, preferred plants or agricultural crops.

What is the most common naturally occurring auxin?

Indoleacetic Acid (IAA)

what Herbivors eat plants?

Insects Birds Mammals

Define Geotropism

It is a growth movement of part of the plant in response to the gravitational pull of the earth.

Define Phototropism

It is a growth response to a light stimulus.

What is Tropic Movement?

It is the plants response to an environmental stimulus which causes the plant to either grow positively towards the stimulus or negatively away from the stimulus.

What does Tropical Movement result in?

It results in Differential Growth.

What does Monocotyledons mean?

Narrow leaf

What are Auxins?

One of the most important groups of plant hormones.

What is the Value of Phototropism?

Phototropism ensures that all leaves of the plant are exposed to light so that photosynthesis can take place.

What do Plant Hormones do?

Regulate Plant Growth, development and differentiation of cells.

What is the theory behind Pruning?

That if you cut the Apical Bud, there will be not sufficient auxin's to stop the lateral buds from growing. as a result the plant will become more bushier.

What role do Microorganisms play in protecting plants?

The Microorganisms play a major role in anti-herbivory as the micro organisms can inflict damage after the thorn has allowed them to get past the animals skin layer. Thus they can keep the animal from coming back to the plant.

What makes Auxins?

The tip of the shoot - Apical Bud constanty makes auxins, while a very small amount is made by the root tip (bottom of plant)

What is another trait the thorns on a plant can have?

They can have warning colouration. Such as the Acacia Karoo which has White thorns.

How do Auxins diffuse?

They diffuse downwards, this creates a gradient along the main axis of the plant. the concentration of Auxins is highest at the tip of the plant and lowest at the roots.

What is the dilemma plants face when it comes to defence mechanisms?

They need to attract beneficial pollinators and seed dispensers while minimising damage caused by herbivores and pathogens.

What is the aim of Physical Defences against Herbivores?

To prevent on grazing and loss of valuable plant mass ( important for plants in arid conditions).

What does Weed killer contain?

high concentrations of Auxins that are used on lawns or crop fields.

Give an example and explain what Antibacterial Chemicals do?

1. In some plans such as Garlic they help counteract Pathogenic Bacteria.

Give an example and explain what Essential Oils do?

1. Dont affect Humans 2. They are posinous to insects and protect the plant from Fungal and Bacterial attack. 3. Example is peppermint and rosemary.

what is the Significance of a Geotropism Experiment?

1. If the Germinating seedlings are placed in a petri disc on a stationary clinostat the roots (radicles) will elongate and bend under the influence of gravity. I.e they will grow downwards. 2. If the Clinostat is wound up the radicles would continue growing in the same direction as when the experiment started as the gravitational force has been eliminated.

Give an example and explain what Bitter Tasting Chemicals do?

1. Alkaloids (found in many plants) 2. Repel Herbivores as they have an unpleasant taste. This stops the herbivores after the first bite. Caffeine is an example and is toxic to insects and fungi.

What does Gibberellic Acid do?

1. Cause elongation of the main stem by causing the internodes to lengthen. (auxins also cause elongation) 2. It stimulates seed germination. As the seed absorbs water the Embryo produces GA, causing a chain of events to take place including endosperm breaking down into glucose. this diffuses into the embryo and is used for plant growth. I.e it encourages the plant to break out of dormancy.

What two procedures do plants take?

1. Chemical Defence 2. Physical Defence

Give an example and explain what Toxins do?

1. Cyanogenic Glycosides which are from the Cassava Plant produces cyanide in the digestive tract that stops cellular respiration. 2. Pyrethrins from the Pyrethrum Flower attacks the nervous system of insects.

Give examples of Chemical Defences

1. Digestive Enzyme Inhibitors 2. Bitter Tasting Chemicals 3. Toxins 4. Stinging Hairs 5. Essential Oils

Explain how Abscisic Acid (ABA) helps the plant.

1. It causes the Stomata to close when the soil water is insufficient to keep up with transpiration. It therefore reduces water loss through Transpiration. 2. It promotes dormancy in both seeds and buds. this stops the seeds from germinating when the conditions are either too cold or too dry. Dormancy will be lifter when conditions are sufficient. It also turns the Apical Bud to a dormant state to protect it from mechanical damage or drying out. 3. It promotes Abscission of leaves and fruit when the conditions are unfavorable.

What does Weed Killer do?

1. Kills the Dicotyledons (broad leaf) by speeding up their growth to such an extent that the plant weakens and dies. 2. Does not harm the Monocotyledons (narrow leaf) such as grass.

Give an example and explain what Digestive Enzyme Inhibitors do?

1. Tannins (found in Fynbos plants) 2. Blocks normal digestion and absorption of proteins by Herbivores.

Explain what will happen in a Phototropism Experiment to the experiment Plant?

1. The stem will have curved as it aims to grow towards the light. I.e it is positively phototropic.

How is the Physical Defence successful against Herbivores?

1. The thorns slow down eating rate and makes it hard to get to the leaves of a plant. 2. The thorns sometimes have Pathogenic Bacteria and Fungi on them which can cause an infection in the animal if it is spiked. As a result the animal could get Tetanus.

Give an example and explain what Allergy Causing Chemicals do?

1. They can cause allergic reaction such as excessive salivation or mouth irritation. This will stop the Herbivore from trying to eat the plant again.

What are the functions of an Auxin?

1. They promote growth by stimulating cell division(mitosis) and cell elongation which will effectively bring about growth. 2. They Cause Apical Dominance 3.They Play a role in Tropic Movements

Explain How Auxin's Promote Growth?

1. They promote growth by stimulating cell division(mitosis) and cell elongation which will effectively bring about growth. Stem tissues that are situated away from the shoot tip become more sensitive to the auxin concentration and as a result they require less auxin's to bring about cell elongation, if the concentration is too high, cell elongation will stop. Root elongation requires less auxin's than the stem and a higher concentration will also stop cell elongation in the roots.

List three physical Defences aimed at stopping Herbivores.

1. Thorns 2. Spines 3. Prickles

List three other Plant hormones besides Auxins.

1.Gibberellins 2.Abscisic Acid (ABA) 3.Weed Control

What do Gibberellins do that Auxins don't?

1.Stimulate growth of side branches from lateral buds. I.e they have nothing to do with Apical dominance. 2.They play no part in the tropic movements of the plant.

Explain what will happen in a Phototropism Experiment to the Controlled plant?

1.The stem of the control plant will remain upright. 2. The control plant has been exposed to light stimulus on all sides and therefore it has grown straight.

Explain Apical Dominance?

2. Auxin's cause Apical Dominance. There is a concentration of Auxin's at the apical bud which stops any growth from lateral buds as the apical bud would be forced to fight for nutrients and light. lower down the plant the concentration of auxin's lessens and these lower lateral buds can produce shoots which can grow into lateral branches which wont affect the apical bud. This results in the plant having a pyramidal shape. If the Apical Bud is removed, the lateral buds will grow because there are no auxin's inhibiting growth. as a result the plant will become more bushier.

Explain how Auxin's are involved in Tropic movements

3. External stimuli bring about Tropic Movements, however Auxin's cause the cell elongation on only one side of the stem or root which results in uneven growth.

Give an example and explain what Stinging Hairs do?

Found on the leaves of some plants. Can cause Immediate and severe burning sensation if touched.

What is the value of Geotropism?

Geotropism helps germinating seedlings as the seed is initially dehydrated and needs to absorb water to grow. Geotropism helps the seedling move in the right direction in the hope of finding water.

Give an example of a Gibberellin?

Gibberellic Acid (GA)

What does Abscisic Acid (ABA) do?

Helps the plant cope with potentially harmful conditions by being a growth inhibitor as it helps the plant adapt to adverse conditions.

How does a plant respond to gravity?

If a seedling is placed horizontally in a dark chamber the shoot will develop upwards while the roots develop downwards.

Where exactly are these hormones found? and in what concentration?

Plants lack glands so they cant produce or secrete hormones, so each cell is capable of producing the needed hormones. These hormones are found in extremely low concentrations.