A2 OCR Biology | F215 Module 4 - Plant Responses

Thorough but straight to the point - A six page PDF on Plant Responses for A2 Biology that are specific to Module 4 of the F215 Chapter in the OCR Biology Specification, of which can be found on the OCR website. Enjoy, hope they're of use!

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Biology A | F215 Module 4 ­ Plant Responses Dean Williams
- Suited to the F215 Specification -
a) Plants need to respond to their environment in terms of predation and abiotic stress to
increase chances of survival for example they may be subject to herbivory where herbivores
will eat leaves that are used to absorb sun light using chlorophyll, which is to be used in
photosynthesis. If leaves are damaged or eaten then a plant cannot absorb sunlight efficiently
and therefore cannot carry out photosynthesis efficiently to make sugars such as glucose to
survive. Plants may produce toxins as a response to predation to increase chances of survival
that deter the predators from eating their leaves. To respond to abiotic stress plants such as
carrots produce anti-freeze proteins that bind to ice crystals and decreases the temperature
that water freezes at meaning these ice crystals cease to grow which mean they don't lower
the temperature to a degree that is too low for enzymes to function.
b) Plants also respond to their environment using directional stimuli called Tropisms which also
allow a plant to increase their chances of survival by respond to its environment. Tropisms can
be Negative or Positive ­ Negative tropisms grow away from a stimulus, Positive tropisms
grow towards a stimulus.
Tropism ­ A plant response to a directional stimulus.
Different types of tropisms include:
- Phototropism, Growth towards or away from sunlight
- Geotropism, Growth of the roots into the soil
- Chemotropism, Growth towards a chemical stimulus
- Thigmotropism, Growth that responds to a touch
c) An example of a positive tropism that increases the chances of survival of a plant is Positive
Phototropism. Plants use Growth Regulators as hormones for Tropisms when reacting to a
stimulus. Auxin is a hormone which has a high concentration in the Apical Bud and is the Plant
Growth Regulator hormone that responds to sunlight during Phototropism. When there is a
change in environment such as an uneven distribution of sunlight that certain areas of the
plant are exposed to, Auxin will unevenly distribute also to compensate for a certain part of
the plant not getting as much sun light as the other. Auxin causes uneven growth of the plant
shoot towards the sunlight as it promotes plant growth ­ Positive Phototropism. Auxin acts
Biochemically by using Indoleacetic Acid, an important Auxin used in Phototropism, to make
the cellulose cell walls of the cells on the shaded side of the plant more acidic and more
permeable to H+ ions which means the bonds between the sugar molecules within the
structure of the cell wall are weakened which allows the shape of cells to change and stretch
therefore allowing the plant to bend and grow in the direction of sunlight.

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Biology A | F215 Module 4 ­ Plant Responses Dean Williams
- Suited to the F215 Specification -
d) Apical Dominance ­ The Apical Bud at the tip of the shoot inhibits growth of the Lateral Buds
further down the plant.
Apical Dominance inhibits Lateral Buds (Side Shoots) from growing and also saves energy.…read more

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Biology A | F215 Module 4 ­ Plant Responses Dean Williams
- Suited to the F215 Specification -
4. The conclusion should state that:
These results showed that removing the tips of shoots caused extra side shoots to grow
because of the low Auxin concentration unable to inhibit the growth of the Lateral Buds
(Side Shoots).…read more

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Biology A | F215 Module 4 ­ Plant Responses Dean Williams
- Suited to the F215 Specification -
3. Both sets of plants should be left to grow for 28 days in the same conditions such as light
intensity and the same amount of water regularly so no variables affect the results. After
28 days a results table should be made comparing stem lengths at the beginning and end
of the experiment.…read more

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Biology A | F215 Module 4 ­ Plant Responses Dean Williams
- Suited to the F215 Specification -
e) Leaf Abscission is a response to Abiotic stress that is triggered by the shortening of days, when
there is less daylight within a day, during the transition to winter through autumn.…read more

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Biology A | F215 Module 4 ­ Plant Responses Dean Williams
- Suited to the F215 Specification -
Rooting powder which also contains Auxins can be used to make many cuttings of different
plants or the same plants form new roots and grow into whole new plants. Because Auxins can
also make Roots Negatively Phototropic as well as making shoots and the Apical Bud Positively
Phototropic, it promotes growth of roots that grow away from sunlight.…read more

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