GENETICS AND ADAPTATION

GENETICS AND ADAPTATION Obtaining Food and Coping with Dangers Mr G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

2. Finding a mate • Plants have to employ the services of wind, animals and even water to transfer their gametes. G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

Competition • Some plants are so dense that no other plant can survive beside them due to lack of light. G Davidson

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 . G Davidson

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 G Davidson

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. G Davidson

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. G Davidson

Sun and Shade Plants • Plants undergo photosynthesis during hours of light. • They are also undergoing respiration. G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

Defence Mechanisms • Some plantshave 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,theback of the knees) most rapidly, and these areas may remain highly sensitive to the oil for uptoone year.Even minute amounts of the oil may trigger flare-ups weeks after the rash is healed. G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

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. G Davidson

GENETICS AND ADAPTATION