A2 OCR Biology Responding to the Environment

All the notes you need for A2 OCR Biology Responding to the Environment

HideShow resource information
  • Created by: h
  • Created on: 12-06-12 16:11
Preview of A2 OCR Biology Responding to the Environment

First 239 words of the document:

A2 Biology Revision Notes Responding to the Environment
aWhy plants respond to the environment
Animals respond to the biotic (living) and abiotic (non-living) components of their environment. Plants
also respond to external stimuli. Responding to the environment in this way may help the plant to
avoid stress of avoid being eaten, and to survive long enough to reproduce.
Tropisms
Tropism ­ a directional growth response in which the direction of the response is determined by the
direction of the external stimulus
Tropisms include;
Phototropism ­ shoots grow towards light (positively phototrophic), enabling them to
photosynthesise
Geotropism ­ roots grow toward the pull of gravity. This anchors them in the soil and helps
them to take up water
Chemotropism ­ on a flower, pollen tubes grown down the style, attracted by chemicals,
towards the ovary where fertilisation can take place
Thigmotropism ­ shoots of climbing plants, such as ivy, wind around other plants or solid
structures and gain support
Chemotropism
Plant hormones and their effects
Hormone Effects
Auxins e.g. IAA Promote cell elongation, inhibit growth of
side-shoots, inhibit leaf abscission (leaf fall)
Cytokinins Promote cell division
Gibberellins Promote seed germination and growth of stems
Abscisic acid Inhibits seed germination and growth, cause
stomatal closure when there is low water
availability
Ethene Promotes fruit ripening
1

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

A2 Biology Revision Notes Responding to the Environment
How plants respond to the environment
Auxins
Auxins stimulate shoot growth by cell elongation.…read more

Page 3

Preview of page 3

Here's a taster:

A2 Biology Revision Notes Responding to the Environment
This increases production of cellulose, which digests the walls of the cells in the abscission
zone
Controlling plant growth
Apical dominance
Apical dominance ­ the growing apical bud at the tip of the shoot inhibits growth of lateral buds
further down the shoot
If you break the shoot tip (apex) off a plant, the plant starts to grow side branched from
lateral buds that were previously dormant.…read more

Page 4

Preview of page 4

Here's a taster:

A2 Biology Revision Notes Responding to the Environment
Researchers compared GA concentrations of tall pea plants and dwarf pea plants, which
were otherwise genetically identical. They found that plants with higher GA concentrations
were taller
To show that GA directly causes stem growth, researchers needed to know how GA is
formed.
o The worked out that the tall allele (Le) was responsible for producing the enzyme
that converted GA to GA.…read more

Page 5

Preview of page 5

Here's a taster:

A2 Biology Revision Notes Responding to the Environment
Brewing
To make beer you need malt
When barley seeds germinate, the seed produces amylase enzymes that break down stored
starch into maltose
Usually the genes for amylase production are switched on by naturally occurring gibberellins
Adding gibberellin can speed up the process
Sugar production
Spaying sugar cane with gibberellins stimulates growth between the nodes, making the
stems elongate.…read more

Page 6

Preview of page 6

Here's a taster:

A2 Biology Revision Notes Responding to the Environment
Restricting ethene's effects can also be useful. Storing fruits in low temperature with little
oxygen and high carbon dioxide concentrations prevent ethene synthesis and so prevents
fruit ripening. This means fruit can be stored for longer.…read more

Page 7

Preview of page 7

Here's a taster:

A2 Biology Revision Notes Responding to the Environment
o Joints
Medulla oblongata
Controls action of smooth muscle in the gut wall, controls breathing rate and heart rate
It is effectively in control of the autonomic nervous system
Regulatory centres for a number of vital processes are found in the medulla oblongata
including;
o Cardiac centre, regulating heart rate
o Respiratory centre, controlling breathing and regulating rate and depth of breathing
Hypothalamus
Controls the autonomic nervous system and endocrine glands
Controls most of the body's homeostatic…read more

Page 8

Preview of page 8

Here's a taster:

A2 Biology Revision Notes Responding to the Environment
Sensory and motor systems of the peripheral nervous system
Sensory neurones carry impulses from the many receptors, in and around the body, to the
CNS
Motor neurones carry impulses to the CNS to the effector organs
Many neurones are bundled together and covered in connective tissue to form nerves.…read more

Page 9

Preview of page 9

Here's a taster:

A2 Biology Revision Notes Responding to the Environment
Action of muscles
Muscles produce a force when they contract. The movement of any bone at a joint requires the
coordinated action of at least two muscles.
Movement at the elbow joint
The biceps and triceps muscles act
antagonistically to move the forearm at
the elbow
The elbow joint is a synovial joint. These joints
occur where a large degree of movement is
required.
The synovial fluid is a lubricant.…read more

Page 10

Preview of page 10

Here's a taster:

A2 Biology Revision Notes Responding to the Environment
The motor unit
Some muscular movements require a stronger contraction than others. The brain controls the
strength of contraction as many motor neurones stimulate a single muscle. Each one branched to
neuromuscular junctions, causing the contraction of a cluster of muscle cells (called a motor unit).…read more

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all resources »