What is adaptation?
All members of a species are slightly different from one another. They show variation. Any variation that helps the organism survive is an adaption. The organism is adapted to its environment.
The process of evolution works by selecting particular adaptations to survive from one generation to the next. An individual that has a characteristics which helps it survive in its environment is more likely than an individuals without characteristic to live long enough to reproduce. Over a long period of time - very many generations - more and more individuals in the population will have that characteristic, as those that did not will have died out. The characteristic is an adaptation. We say that the adaptation has been selected.
Adaptations help the organism cope with environmental stresses nd obtain the things they need to survive. A well adapted organism will be able to:

find enough water

find enough food or photosynthesise well

gather enough nutrients

defend itself from predators and disease

survive the physical conditions of its environment, such as changes in temperature, light and water levels

respond to changes in its environment

still have enoug energy left over to reproduce successfully

How do adaptations enhance survival?
Behavioural Adaptation
A behavioural adaptation in an aspect of the behaviour of an organism that helps it to survive the conditions it lives in. For example, when you touch an earthworm it quickly contracts and withdraws into its burrow. The earthworm has no eyes, so this is a behavioural adaptation to prevent being eaten.

Physiological/Biochemical Adaptations
A physiological or biochemical adaptation is one that ensures the correct functioning of cell processes. For example, the yeast Saccharomyces can respire sugars anaerobically or aerobically to obtain energy, depending on how much oxygen there is in the environment. Producing the correct enzymes to respire the sugars present in their environment
is a physiological/biochemical adaptation.

Anatomical Adaptations
Anatomical means strucural. Any structure that enhances the survival of the organism is an adaptation. For example, many bacteria (Legionella) have flagella that enable them to move idependently. This flagellum is a structural adaptation.

An example of adaptation: xerophytic plants
Behaviour Adaptations
Xerophytes respond to a shortage of water in several ways:

some plants close their stomata when little water is availalbe. This conserves water so that they do not wilt.
some plants open their stomata only at night. This conserves water because less will be lost from the leaves at night when it is cooler and the air is more humid
some plants fold or roll their leaves when water is in short supply. This reduces water loss by trapping moist air in the folded leaf, so reducing the water vapour potential gradient for diffusion out of the leaf
some plants even open their stomata when they are in short supply of water. This causes the leaves to wilt and expose less surface area to the sun

Physiological/Biochemical Adaptations
These are the mechanisms by which a plant can open or close its stomata, fold its leaves or store water.
The saguaro cactus has a stem with an accordian-fold structure. During dry periods the folds tighten into ridges and become more pronounced. When water becomes available, the cactus absorbs it from the ground. The water fills the cells of the stem, where it may be stored for years. The cells expand and cause the stem to expand and become more rounded. The accordion folding becomes less obvious.

Anatomical Adaptations
These are structures that enable a xerophyte to survive in very dry conditions. There are many examples of structural adaptations.

the roots may be shallow, but spread out over a wide area. This allows a plants to absorb a lot of water when it is available. A mature saguaro cactus can absorb alomst 750dm3 of water during a brief storm.
The roots may be very long. This enables the plant to reach water that is deep underground. The camel thron tree has roots up to 40m
The stem or leaves may be fleshy - an adaptation to store water
the leaves may be reduced in size - this reduces the surface area for evaporation
the leaves may be very waxy, so moisture can leave the leaf only through the stomata
the leaves may be curled, folded, hairy or have their stomata sunk in pits. These adaptations trap a layer of moist next to the stomata, reducing the water potential gradient for water vapour to diffuse into the atmosphere. All these adaptations reduce water loss by transpiration.

	Criado por siobhan.quirk quase 11 anos atrás

Undergraduate Biology (Biodiversity and Evolution) Notas sobre Adaptation, criado por siobhan.quirk em 27-05-2013.