Biology Notes Form 1 Introduction to Biology Biology is a branch of science that deals with the study of living things. There are diverse forms of life on earth ranging from the invisible microscopic living things to the gigantic life forms. It aims at explaining the living world in terms of scientific principles. It is important to note, however, that living things interact with the non living things in the environment as Well. Biology, therefore also entails the study of non living things as well.
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Attraction of water molecules to the Walls adhesion from the stem water enters the xylem of leaves water moves in the xylem vessels of the stem in a continuous uninterrupted water column up to the tree leaves Leaves once in the leaves water moves into the mesophyll cells by osmosis as water vaporizes from the spongy mesophyll cells their sap becomes more concentrated than the adjacent cells as the result water flows into the cell from other surrounding cells which in turn takes in water from xylem vessels within the leaf veins this creates a pull suction force called transpiration pull that pulls a stream of water from xylem vessels in the stem and roots. The transpiration pull maintains a continuous column of water from the roots to the leaves. Absence of cuticle also increase rate of transpiration ii Explain the environmental factors that affect rate of transpiration in plants high temperature increases rate of transpiration and low temperature reduces the rate humidity when high increases rate and when low reduces the rate transpiration rate is higher in moving air wind than in still air high light intensity increases internal temperature hence higher rate of evaporation leading to higher rate of transpiration availability of water in the soil leads to more absorption hence more loss to the atmosphere atmospheric pressure when high leads to more evaporation and when low leads to low rate evaporation of water iii State the structural differences between xylem vessels and sieve tubes sieve tubes have cross wall while xylem vessels have none xylem vessels are lignified while sieve tubes are not Sieve tubes have cytoplasm elements while xylem vessels have none. Water vapour accumulates in the depression of stomata lowering the water vapour concentration gradient leading to lower rate of evaporation rolling of leaves v State the factors that cause increase in the rate of transpiration from leaves increased light intensity low relative humidity temperature vi Explain how drooping of leaves on a hot sunny day is advantageous to a plant reduces surface area exposed to sun reducing cuticular transpiration c Explain how aquatic and terrestrial plants are adapted to deal with problems of transpiration a. Mesophytes they grow in soils with enough water water loss is perfectly balanced by absorption of more from the soil no special adaptations b.