Surviving With Limited Water Flashcards
Outline the role of water in biological processes.
Life first evolved in aquatic environments and, as a result, water became a key reagent for many metabolic reactions, as well as providing the solvent in which nearly all metabolic reactions take place.
What have some terrestrial organisms developed to remain hydrated and why do all organisms not possess the same adaptation?
A cuticle, an unbroken, waterproof epidermis composed of oily or waxy compounds. An adaptation which allows desert cactus to survive. All organisms don’t have one because it prevents the use of evaporation for temperature control & prevents gaseous exchange with the atmosphere.
Define desert from the perspective of biological survival.
Deserts are defined by their low or unpredictable rainfall, but crucially for survival they are defined by the balance between precipitation and evaporation. Cambridgeshire and Jerusalem have the same annual rainfall but cool English climates retain moisture better.
Roughly how much water does the soft tissue of terrestrial plants contain?
90-95% water
When are stomatal pores in plants open?
Usually only in the light, transpiration ceases at night.
Outline the response triggered in desserts after rains & explain why this happens.
Suddenly bright flowers come into bloom creating vast meadows in what was previously arid, bare soil. These plants must complete their entire life cycle in the brief window after rain & attracting pollinators is vital so competition among blooms is high.
Why do cactuses have thorns?
They are precious reservoirs of water in a dessert & must protect themselves from the threat of thirsty animals.
List some of the adaptations plants have made to living in deserts.
Water storage in succulent leaves & swollen trunks, reflective surfaces (bright white), leaves have thick rinds with few pores, or their are no leaves at all, just photosynthetic stems with pores protected in deep ridges (cactus). Some practice self-amputation in excess drought, or live deep underground with ‘window leaves’.
What kinds of habitats resemble mini-deserts in the UK?
Habitats that resemble mini-deserts in the UK include habitats where there is little or no soil (e.g. on rocks, walls or very shallow soils) and habitats such as sand dunes which drain rapidly and retain little water.
What are the main two strategies of handling water shortage?
Avoidance & tolerance.
What are the different methods of AVOIDING water shortage?
Maximising water supply, water piracy, dormancy & efficient water use & storage.
Outline the main method plants use to maximise water supply.
Incredibly deep taproots (up to 50m) which can reach the water table & bring water up through hydraulic lift to the plant leaves at the surface.
Outline the method of water piracy, allowing desert plant growth.
Shallow rooted plants, such as grasses, which make us of moisture lifted by the hydraulic lift system of deeper rooted shrubs. Water seeps out of the shrub roots overnight and the shallow rooted plants utilise it.
What are ephemerals?
Short-lived plants that reproduce quickly by seed then die.
Outline the dormancy strategy as a method of living with water shortage.
A method of water shortage avoidance where plants fit their entire life cycle into the brief period following rains while water is available, then set seeds, which can last many years, then they die. Others shed their leaves & the entire organism enters a dormant state until the next rainfall.
Define dormancy.
Dormancy comes from the Latin dormire, ‘to sleep’. In biology it is used to describe metabolically inactive organisms, which are usually surviving unfavourable conditions by minimising their resource requirements. It is a common strategy in deserts where the availability of one key resource (water) is spasmodic and often unpredictable.
Do desert plants with short life cycles (seed dormancy strategy) favour C3 or c4 pathways and why?
C4 because it allows very rapid short term growth un-inhibited by the excessive light in desserts. C4 is less energy efficient, but more water efficient than C3. Deserts have abundant sunlight but very little water so C4 is favoured.
Define leaf polymorphism.
The ability of an individual plant to produce more than one type of leaf.
Define ‘succulents’ and outline which photosynthetic pathway they use.
Plants with thick fleshy leaves and stems that store much more water than a non-succulent plant. Succulents generally use the CAM photosynthetic pathway that requires large cells containing large vacuoles to store the organic acid made overnight.
What are resurrection plants?
Plants whose tissues are able to dehydrate while remaining alive. The plant appears dead until water is added, when it rehydrates its tissues and appears to come back to life.
What are Xerophytes?
plants that remain metabolically active during drought by a combination of restricting water loss, efficient water uptake and high tolerance of low tissue water content. Typical examples are evergreen desert shrubs and grasses.
