4.6 Role of water  (Page 2/3)

Design your own xerophyte

• Draw a sketch to show the adaptations if you were to do the design.

Assessment of DESIGN

Were you able to DRAW a meaningful DESIGN with logical adaptations? [LO 1.3]

Animals:

With animals, in contrast to plants, both structural modifications and behavioural adaptations are used to survive drought. Most of the adaptations are intended to limit loss of water so that the animal needs to ingest less water to survive. In some cases the animal has developed a mechanism for storing water.

Examples of structural adaptations

• Skin cover

• Insects and spiders have a plastic or leathery skin cover (external skeleton) that permits no water to penetrate. This limits their need for water to such a degree that the moisture that they ingest with their food is sufficient.
• Reptiles’ skin has also been adapted to limit loss of water to the minimum. In the case of other animals where the skin needs to be moist for other reasons, there are mechanisms that prevent unnecessary loss of water. In the case of frogs, for example, mucous is secreted.
• Birds have a sebaceous gland at the base of the tail. This gland secretes oil that spreads all over the body and makes the feathers relatively waterproof. (You may have seen your mother removing the little gland from the chicken before cooking it.)
• In the case of mammals the skin could be adapted to limit water loss to a minimum. For instance, dogs perspire through their tongue and not through their skin. That is why they pant when they are hot.

• Internal adaptations

• Animals’ digestive systems and excretory systems have also been adapted to regulate water loss. In the colon, for example, much of the water that is still present in food residues in the body, is absorbed before defecation takes place. The kidneys determine how much water should be allowed to pass to the bladder before it is excreted.
• Camels have been specially adapted to survive for long periods without ingesting water: water is stored in the hump in the form of a chemical compound and can be released when necessary.

Examples of behavioural patterns

• The evaporation of water is a common cooling mechanism in animals. Humans, for example, must be able to perspire so that the evaporating perspiration can prevent rapid rising of body temperature, whether it be as a result of heat or of heavy exercise. Animals often demonstrate behavioural patterns through which the body is kept cool so that cooling down through other mechanisms, e.g. perspiring, is not necessary. For instance, they might seek out a shady area, dig tunnels, lie under the sand, be inactive during the day or even migrate or hibernate in summer.

Assignment:

Read up more on this subject and describe FIVE more ways in which plants prevent water loss and FIVE ways in which animals prevent water loss.

Assessment

LO 1: Scientific investigations:

The learner will be able to act confidently on curiosity about natural phenomena, and to investigate relationships and solve problems in scientific, technological and environmental contexts.