Transcript GENETICS AND ADAPTATION

GENETICS AND
ADAPTATION
Obtaining Food and Coping with
Dangers
Problems with plant sessility
(the inability to move)
Animals move to forage for food,
escape danger, find a mate, seek shelter
and defend themselves.
They may even use movement as a
means of regulating metabolism e.g.:
 we shiver to get warm.
Reptiles bask in the sun to bring up their
body temperature.
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Problems with plant sessility
(the inability to move)
Most of this activity is related to the
need to minimise energy loss.
The same needs apply for plants but
they are not mobile, therefore they
must overcome these problems.
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1. Obtaining food, water and
minerals
Photosynthetic rate is determined by
the availability of light, water, carbon
dioxide and minerals, as well as being
limited by temperature.
When any one of these factors is
limiting, a plant will starve unless it can
evolve ways of overcoming the shortage.
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1. Obtaining food, water and
minerals
A plant’s leaves are often arranged so
that over-shading of one leaf by
another is reduced to a minimum.
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1. Obtaining food, water and
minerals
Such a pattern is called a leaf mosaic
and it allows the maximum surface area
of leaves to receive light.
This makes the floor of broad-leafed
woodlands very dark and explains why
the shade plants flower in spring before
the leaf canopy grows to shut out the
light.
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1. Obtaining food, water and
minerals
In order to reach up to where there is
more light, some plants such as ivy have
become climbers.
Trees such as oak and birch have
become perennial (produce permanent
tissue every year), and so reach the
light by being taller.
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1. Obtaining food, water and
minerals
 Shade plants such as wood sorrel,
crocus and bluebell have developed a
metabolism and life cycle to enable
them to survive in poorly lit areas.
 Insectivorous plants trap and digest
insects in order to obtain essential
nitrogen.
 Thus they can live in nitrogen deficient
soil.
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2. Finding a mate
Plants have to employ the services of
wind, animals and even water to
transfer their gametes.
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2. Finding a mate
Insect pollinated plants, i.e. primrose,
have bright petals, scent and nectar to
attract insects and other animals in
order to pick up pollen and pass it from
flower to flower.
Grasses, however, have no such
attractive flowers, but feathery
structures instead as they rely on the
wind to transfer their pollen.
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3. Shelter
Plants can’t shelter from the extremes
of wind, rain and temperature, neither
can they avoid the possibility of being
eaten or destroyed by fire.
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3. Shelter
Where severe weather is a hazard,
plants develop sturdy root systems and
remain stunted to avoid exposing a large
surface area.
The bristle cone pine can grow in a hostile
climate at altitudes over 7000ft.
Cactus survive where there is very little
water.
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3. Shelter
Some specimens are reckoned to be the
oldest living things on Earth today,
reaching ages of up to 6000 years old.
Eucalyptus trees are exceptional in
their tolerance to a large range of
extremes.
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3. Shelter
Many types can regenerate very rapidly
after fire.
Some types will only grow after flood
and yet other are used in afforestation
schemes on the edge of the Sahara
desert.
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4. Overcrowding
Plants have developed ways of seed
dispersal to prevent overcrowding.
Coconuts can travel thousands of miles
over the oceans before reaching land to
germinate into a palm tree.
Rose bay willow herb produces hundreds
of seeds each with its own little
parachute which can be carried off in
the wind.
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Competition
 Plants compete with each other for
light, water and soil nutrients.
 Plants of the same species, when grown
together, are in direct competition with
each other if any of the above
resources is limiting.
 This results in intraspecific
competition and leads to many plants
growing more slowly.
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Competition
This is overcome by gardeners spacing
seeds when planting and then thinning
out after germination occurs.
Plants of different species in the same
habitat often require different
resources.
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Competition
 This is called interspecific competition
and is usually not as fierce as
intraspecific.
 However, some plants can become
dominant over others and the others
have to adapt to survive e.g..
 Flower before the dominant plant grows.
 Evolve more efficient photosynthetic
pigments.
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Competition
Some plants are so dense that no other
plant can survive beside them due to
lack of light.
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Competition
 Some plants even produce poisons which
prevent other plants growing beside them.
 The walnut tree and many desert shrubs reduce
competition from neighboring plants with a
poisonous compound that washes off leaves and
onto plants underneath and kills them
 Grazing can have an effect on the numbers
of a plant species because the plants never
get the chance to grow tall and dominate
other plants by shading them .
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Competition
Rabbits, for example are unselective
grazers, i.e. they eat most plants.
Sheep, however, are more selective,
since they eat only grass.
Properly grazed land therefore has a
higher biodiversity of plants than ungrazed
land.
Overgrazing of course reduces biodiversity
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Sun and Shade Plants
Some plants require bright light in
order to thrive, whilst others can grow
successfully in dimly lit areas.
Grass is a sun plant requiring a lot of
light to grow well, so is only found in
open areas.
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Sun and Shade Plants
Woodland trees are shade tolerant
plants, as most of their leaves are in the
shade.
Typical shade species are usually found
on the woodland or forest floor where
light is scarce for most of the year.
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Sun and Shade Plants
Plants undergo photosynthesis during
hours of light.
They are also undergoing respiration.
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Sun and Shade Plants
At certain light intensities, the rate of
photosynthesis equals the rate of
respiration and this is called the plant’s
compensation point which varies from
plant to plant.
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Sun and Shade Plants
At this point, the carbon dioxide
produced by respiration is equal to the
carbon dioxide used for photosynthesis
and the same for oxygen.
The compensation period is the time
taken for a plant to reach its
compensation point after being in the
dark.
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Defence Mechanisms
 Many plants have evolved a surprising
variety of strategies to avoid being
grazed:
 Stinging nettles and thorny roses are not
exactly friendly plants.
 Many hundreds of people die each year
from being poisoned accidentally or
deliberately by plants such as deadly
nightshade, hemlock, or the death cap
fungus.
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Defence Mechanisms
Structural adaptations have been
designed by plants to keep animals from
eating them,
e.g. thorns, which have been modified.
Other plants use spines as their leaves
and are so abundant that the plant is
almost untouchable
e.g. gorse, holly, monkey puzzle trees etc.
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Defence Mechanisms
 Some plants have hairs, containing irritating
chemicals e.g. nettles and, in America, poison ivy:
 "The sap of Poison Ivy contains urushiol and causes
immediate primary irritation of the skin, the degree of
burning and irritation depending on the amount of oil
involved. Meanwhile, the resin quickly penetrates the skin
and triggers an allergic reaction. It penetrates thin skin
(eyelids, between the fingers and toes,the back of the
knees) most rapidly, and these areas may remain highly
sensitive to the oil for up to one year. Even minute amounts
of the oil may trigger flare-ups weeks after the rash is
healed.
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Defence Mechanisms
As well as structural adaptations, some
plants also have the ability to produce
protective chemicals.
Some plants produce chemical mimics,
some of which are serious to the animal
consuming it, e.g. some substances
reduce animals fertility which reduces
future damage to the plants.
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Defence Mechanisms
Poisons like hydrogen cyanide are
produced by a number of plants, e.g.
white clover.
The production of cyanide called
cyanogenesis results when the leaves of the
plants are damaged.
Many plants, such as rhubarb and wood
sorrel, produce oxalic acid which is a
metabolic poison.
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Effects of Grazing
Newly planted woods need to be fenced
off to prevent grazing herbivores such
as deer and rabbits from damaging the
young saplings.
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Effects of Grazing
Grasses have an advantage as they have
very low growing points which enable
them to produce new leaves even though
the old ones have been eaten.
Some plants, such as daisies and
dandelions, also produce leaf rosettes
very close to the ground to avoid being
eaten.
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