Plant responses to abiotic and biotic components of their environment.
Abiotic
components
e.g.
Biotic components
e.g.
Plant responses to herbivory:Biotic component – _________________ are animals that eat plants (any plant eating animal from insects to
elephants). Plants cannot escape being eaten so have evolved a wide range of defences to prevent and minimise
damage by ____________________ (the process by which herbivores eat plants)
https://www.youtube.com/watch?v=Hja0SLs2kus
Physical defences
such as _____________, spikes, barbs,
spiny leaves, inedible tissue, hard
covering to protect seeds.
Chemical defences
Match the correct chemical with its defence
Chemical Defence
How they help in defence against herbivores
Tannins
Are chemicals released by one individual that can affect the ___________________ or
physiology of another. For example, cotton plants releasing __________________ when
being eaten by caterpillars attracts parasitic ______________ to lay eggs in the caterpillars.
Alkaloids
A large group of very __________________ tasting, nitrogenous compounds. They tend to be
located in growing tips and ____________, and peripheral cell layers of stems and roots.
Many can act as drugs, affecting the metabolism of animals and sometimes poisoning them.
Pheromones
Toxic to microorganisms and larger herbivores. In leaves, they are found in the
____________ _________________ and make the leaf taste bad. In roots they prevent the
infiltration by ___________________ microorganisms.
Other examples of plants using pheromones (volatile organic compounds).
The cabbage, the cabbage white caterpillar and the parasitic wasp.
When cabbages are attacked by the caterpillars (of the cabbage white butterfly)
the cabbages produce a chemical signal which attracts a parasitic wasp. The
wasp lays its eggs in the caterpillar which develop inside the caterpillar. The
entire content of the caterpillar’s body is eaten before spinning their own tough
cocoon to pupate in, before emerging as another adult wasp.
Folding in response to touch
Most plants move so slowly you cannot follow the movement with the naked eye. There are some exceptions:https://www.youtube.com/watch?
v=nPf3FbR6eQE Mimosa pudica
Sundew plant
https://www.youtube.com/watch?v=
b86SG9Y8Hk4
Venus fly trap
https://www.youtube.com/watch?v
=O7eQKSf0LmY
How does the Mimosa pudica curl up when touched? Current research suggests the following:-
Scientists believe that when the leaf is touched it results in something similar to an ___________ potential
which causes the _____________ transport of potassium ions into the cells on the flexor side of the
pulvinus. In the diagram above the cells on the flexor side are in the bottom part of each pulvinus. The
active transport of potassium into the cells on the flexor side create a water potential _____________ so
water will move into the cells (follow the potassium ions) on the flexor side of the pulvinus by
_______________. The _______________ pressure in these cells increases and as a result the leaflet or
whole leaf bends. When the plant recovers, the situation is reversed – potassium ions return to their
resting levels and water leaves the flexor cells by osmosis.
This movement of the plant may scare the herbivore or make the plant look less appealing to eat.
active
osmosis
gradient
turgor
action
You don’t
have to
remember
these facts.
This has
potential
for an
application
question.
Plant Growth responses
Tropism – is a directional _______________ response in which the direction of the response is determined by the
direction of the external _____________________.
Plants must be able to grow and respond to variations in environmental conditions.
Match the correct tropism to its description
Do not confuse tropic with trophic
Type of tropism
Description
phototropism
Shoots of climbing plants such as ivy, wind around other plants or solid structures to gain
support
Shoots grow towards light (they are positively phototropic), which enables them to
photosynthesise
Roots grow towards the pull of gravity (positively geotropic). This helps to anchor the plant in
the soil enabling them to take up water, which is needed for support (to keep cells
___________), as a raw material for ________________ and to help cool the plant. There will
also be minerals, such as nitrate in the water, needed for the synthesis of ___________
___________. Shoots will grow away from the pull of gravity, shoots are negatively
__________________.
geotropism
chemotropism
thigmotropism
On a flower, pollen tubes grow down the style, attracted by chemicals, towards the ovary
where ________________________ can take place.
Plant hormones coordinate the plant responses to environmental stimuli. They are chemical ________________
that can be transported away form their site of manufacture to act on target cells binding to specific
_______________ on the cell surface membrane by ________________fit. Plant hormones are produced in a
variety of tissues in the plant and can have different affects on different tissues. Plant hormones can influence cell
___________, cell elongation or cell ________________________. Hormones move around the plant in any of the
following ways:- active ______________, diffusion and ___________ _____________ in the phloem or in
________________ vessels.
mass flow
complementary
transport
receptors
messengers
division
differentiation
Complete the table below on the different types of hormones and their effects
Hormone
Cytokinins
(not to be confused
with cytokines)
Effects
Promotes fruit ripening
Promotes seed germination and growth of stems
Auxins
e.g.
________________


Inhibits seed germination and growth.
Causes stomatal closure when the plant is stressed by low water availability.
Plant cell walls limit cells’ ability to divide and expand. Growth only happens in particular tissues in the plant
where there are groups of immature cells that are still capable of dividing, called _______________.
The diagram shows the different meristems in plants.
Use your book to help you complete the table below
Type of meristem
Apical meristem
Description
Lateral bud meristem
Lateral meristems
Intercalary meristems
How Auxins work - Remember this from GCSE?
Rules to remember!
Auxin stimulates elongation of cells in a shoot but inhibits cell elongation in the cells in a root
Auxins – A Level
Use your class book or doddle to write down the mechanism of auxin’s effect.
Auxins are produced at the _____________ of the shoot. The auxin moves to the cells in the zone of
___________________, causing them to elongate, and making the shoot _________________. When light is equal on
all sides, the auxin simply promotes shoot growth ___________________.
evenly
elongation
apex
grow
Use your knowledge on auxins to explain the results of these famous experiments.
Geotropism
The clinostat continually rotates the germinated seeds.
The diagram shows the roots of the germinated seeds.
The germinated seeds on the right of the diagram are
not rotated at all.
Can you explain the results seen in the diagram to the
left?
Auxins and cell elongation
Auxins that are synthesised in the
__________________ cells. Auxins
________________ away from the tip
and bind to _________________ sites.
Vacuoles form and H+ are actively
transported by ATP_______ enzyme on
the plasma membrane into the cell
_____________. This lowers the
________ creating optimum conditions
for wall loosening enzymes to work. The
_______________ in the cell walls is
broken down, the wall becomes less
________________ and can expand as
the cell takes in more water and the
vacuoles fill.
If light is evenly distributed over the
shoot then it will grow straight up.
Auxins and apical dominance
The apical bud secretes ____________,
which _____________ growth in lower
side stems by inhibiting the lateral buds
from growing. If the tip is removed then
the plant starts to grow side branches
form ______________ buds.
inhibits
auxins
lateral
Pruning removes the apical meristem which
means the lateral buds can now grow.
Gibberellins
In Japan, a fungus causes a disease which makes
rice plants grow very tall. The fungal compounds
involved are gibberellins and include gibberellic
acid (GA3).
Scientists have also applied gibberellic acid to
dwarf varieties of plants and they grew taller.
This suggests gibberellic acid causes stem
elongation.
Further investigations have shown that
gibberellins cause growth in the internodes by
stimulating cell____________ and cell
____________________.
elongation division
Gibberellins and seed germination
In seed germination, what secretes gibberellins?
What triggers their production?
What is the source of ATP?
What is the ATP needed for?
What do gibberellins do?
What does ABA do?
What is the experimental evidence that gibberellins are needed for germination of seeds?
Leaf Abscission
Leaf Abscission – is caused by reduced levels of _________________ and increased levels of _________________.
The part of the leaf stem that breaks when the leaf is shed is called the __________ ___________.
Normally __________ inhibits leaf abscission by acting in this __________.
The abscission zone is made up of an _____________ layer and a _______________ layer.
When leaves age (leaf senescence) ______________ production at the ____________tip is reduced. This causes an
increase in ____________ production and makes the cells in the ____________ zone more sensitive to
______________.
Ethene increases the production of __________________ which digests cell _________ in the abscission zone by
causing the leaf to fall.
Stomatal closure
Abscissic acid (ABA) is a key hormone that regulates water status and stomatal movement. Under drought conditions,
plants produce and accumulate increased concentrations of ABA in the guard cells, and this induces stomatal closure
to conserve water.
Summary of some of the hormones and their functions