Biology Questions and Answers Form 2

K.C.S.E Online Revision

KCSE Revision Questions and Answers

Biology Notes Form 2

1. a) i) Define transport

Movement of substances from one pan of the body to anotherii) Explain the necessity of transport in plants and animals
make nutrients move from one point to another
movement of respiratory gases i.e. oxygen and carbon IV oxide
elimination of metabolic wastes
movement of hormones
movement of water
movement of salts
movement of enzymesb) i) Describe the structure and function of root hair
root hairs are found near the root tip
they are cells with elongated ﬁnger-like projections which are in contact with soil particles
they are permeable to water and mineral salts hence are used to absorb Water and mineral salts
There large number offers a large surface area for absorption of water and mineral salts.ii) State ways in which the root hairs are adapted to their functions
the root hair is long/narrow/numerous to increase surface area for absorption of water and mineral salts
many mitochondria in cytoplasm to supply energy for active transport of mineral salts
are thin walled to speed up rate of absorption of Water and mineral saltsc) i) Compare the internal structure of a dicotyledonous root and a monocotyledonous root

Monocot root
ii) State the similarities and differences between a dicotyledonous and monocotyledonous root
Similarities
both used for anchorage and absorption of water and mineral salts
both have root hairs, epidermis, pericycle, cortex, endodermis and vascular bundles
(xylem and phloem)
both may be used to store food/storage organsDifferences
Monocotyledonous
phloem and xylem are arranged in ring form alternately
pith presentDicotyledonous
phloem lies between radial rays of central xylem(star shaped)
pith absentiii) Compare the internal structure of a monocotyledonous and dicotyledonous stem
Monocotyledonous stem

Dicotyledonous stem

i) Give the similarities and differences between a monocotyledonous and dicotyledonous stem
Similarities
both are used for protection
both conduct water, salts and food
both have epidermis, cortex, pericycle and vascular bundlesDifferences
Monocotyledonous
vascular bundles are many and scattered
some have hollow pith or pith is absent
no cambium layer therefore cannot
undergo secondary growth very
little cortexDicotyledonous
vascular bundles are few and arranged in a concentric ring near the epidermis
pith large and well developedState the differences between the internal structure of a root and a stem.
no cambium layer therefore cannot
undergo secondary growth
very little cortex
presence of cambium therefore
undergoes secondary growth
cortex has several layers of cellsc) i) Name the transport structures of a flowering plant
xylem vessels and tracheids transport water and mineral salts from the soil
Phloem vessels translocate manufactured food from leaves to other parts of the bodyii) State the ways in which xylem vessels are adapted to their function
lignified/thickened to prevent collapsing
narrow to facilitate capillary
no cross walls for continuous ﬂow/column of water
have bordered pits for lateral movement of watera) i) Why do ﬂowering plants need water?
photosynthesis
transport
turgidity w h helps in plant support
solvent i.e. medium for chemical reactions
cooling effect during transpiration
seed germinationii) Describe the movement of water from the soil to the leaves of a tall plant
Soil water exists as a thin film in the soil, between soil particles
the concentration of cell sap of root hair is greater than that of the surrounding solution in the soil, thus drawing the Water molecules across the cell wall and cell membrane into the root hair by osmosis
water drawn into the root hair cell dilutes the cell sap making it less concentrated than that in the adjacent cortex cells of the root
due to osmotic gradient water moves from the root hair cells into the cortex by osmosis, from cell to cell by osmosis, across the endodermis by active transport into xylem vessels of the root that conduct water into xylem vessels of the stem into xylem vessels of the leavesStem
Once in the stem water moves up the plant aided by the narrowness of the xylem vessels (capillary), root pressure, attraction of water molecules to each other (cohesion).
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 leavesLeaves
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.iii) Name the process by which mineral salts enter into a plant
active transport
diffusioni) Explain the forces that make water and mineral salts move through a plant
mineral salts are taken up due to diffusion because of the concentration gradient between the mineral ions in sap and those in soil solution
active transport involves energy in form of ATP due to respiration which forces mineral salts through a plant against a concentration gradient
water moves by osmosis through a semi-permeable membrane of root hairs and between cells of stem
in stem water moves by cohesion(attraction of water molecules to each other)
it also moves by adhesion(attraction of water molecules to walls)
capillarity is due to narrowness of xylem vessels
transpiration pull occurs When Water vapour evaporates from sub-stomatal chambers into the air
root pressure is a force that pushes Water up the stem from the roots and causes guttation /exudationii) Explain the uptake of mineral salts by plants
plants require mineral salts for metabolism and proper functioning of their bodies
mineral salts are taken up from the soil into the root hairs in form of solution by active
transport which requires energy
active transport involves substances called carriers taken up together with water and are then carried to the stems and leaves
the main process involved in uptake and movement of mineral salts is active transportb) i) What is transpiration?
loss of water from plant to the atmosphereii) Name the sites through which transpiration takes place in a plant
stomata (stomatal transpiration)
lenticels (lenticular transpiration)
cuticle(cuticular transpiration)iii) State the importance of transpiration to plants
cooling the plant
transport of water
transport of mineral salts
excretion of excess Water from plantsexcess transpiration causes wilting
i) Explain the structural factors that affect the rate of transpiration in plants
number of stomata i.e. the more the stomata the higher the rate and vice versa
turgidity of the guard cells which control the opening and closing of stomata when they are open transpiration rate is high
size of leaves where the larger the surface area the higher the rate of transpiration
leaf fall leads to lower rate of transpiration and also drying of leaves reduces rate of transpiration
Thin cuticle reduces distance through Which water vaporizes hence increase transpiration rate. Absence of cuticle also increase rate of transpirationii) 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 wateriii) 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.iv) State the adaptations of plants which enable them to reduce water loss
thick waxy cuticle
reduced leaf size/thorns/spines
shedding of leaves
Sunken stomata. Water vapour accumulates in the depression of stomata lowering the water vapour concentration gradient leading to lower rate of evaporation
rolling of leaves