Plants

Question 1

Cuticle structure & function

Answer 1

Waxy and transparent, no chloroplast, reduces water loss through evaporation from leaf and prevents invasion of bacteria or viruses

Question 2

Epidermis structure & function

Answer 2

Single layer of closely packed cells, covered on outside with cuticle, protects inner cells and allows light to pass through

Question 3

Palisade mesophyll structure & function

Answer 3

Long and cylindrical, contain largest number of chloroplasts to absorb light energy for photosynthesis. Nearest to upper epidermis and closely packed.

Question 4

Spongy mesophyll structure and functions

Answer 4

Irregularly shaped cells which contain chloroplasts, loosely packed with large intercellular air spaces among cells to increase surface area for gaseous exchange covered with thin film of moisture and contain vascular bundle

Question 5

Vascular bundle structure and functions

Answer 5

Contains xylem and phloem, xylem transports water and mineral salts to mesophyll cells and phloem transports sucrose and amino acids away from leaf to other parts of plant

Question 6

Large intercellular air spaces functions

Answer 6

Allow circulation of air inside leaf for photosynthesis and respiration, interconnecting system of air spaces allow rapid diffusion of CO2 and O2 into and out of cells

Question 7

Guard Cells functions

Answer 7

Contain chloroplasts and regulate size of stomata for gaseous exchange and transpiration, cell wall near stoma is thicker.

Question 8

Reason for stomata being present

Answer 8

Open in presence of light, allowing carbon dioxide to diffuse in and oxygen to diffuse out of leaf

Question 9

Reason for more chloroplasts in upper palisade tissue

Answer 9

More light can be absorbed near leaf surface for photosynthesis

Question 10

Reason for chloroplasts containing chlorophyll

Answer 10

Chlorophyll absorbs energy from sunlight and transfers it to chemical stores of energy in glucose molecules

Question 11

How do guard cells control size of stomata in day

Answer 11

Guard cells photosynthesise, chemical energy pump K+ into guard cells from neighbouring epidermal cells, conc of K+ ^ in guard cell, water potential lowered, water from neighbouring cells enter guard cells by osmosis, guard cells swell and become turgid, due to difference in thickness of cell wall, one side expands more than other, stoma opens

Question 12

How do guard cells control size of stomata in night

Answer 12

K+ move out of guard cells via diffusion, water potential in guard cell decreases, water moves out of guard cells by osmosis, become flaccid, stoma closes

Question 13

Use of stomata in gaseous exchange

Answer 13

Allows exchange of CO2 and O2 with atmosphere

Question 14

Use of vascular bundles in transport

Answer 14

Network is extensive, provides effective transport of water and mineral salts from roots to leaves through xylem and sucrose and amino acids away from leaves to other parts of plants

Question 15

Definition of cambium

Answer 15

Contains undifferentiated cells which can divide to form new phloem and xylem

Question 16

How are xylem vessels formed

Answer 16

When cells, arranged end-to-end are matured and cross wall in adjacent cells is removed. Cell membranes and cellular contents break down, forming long continuous and hollow tubes

Question 17

Structural adaptation of xylem

Answer 17

Empty lumen, consisting of dead cells, reduces resistance to flow of water

Question 18

Use of inner walls of xylem being strengthened by lignin deposits

Answer 18

Provides mechanical support for plant, prevents collapse of vessel and allows it to provide mechanical support to plant

Question 19

Define translocation

Answer 19

Process of transporting manufactured food substances such as sucrose and amino acids in phloem

Question 20

Structure of phloem

Answer 20

Composed of sieve tubes, columns of specialised cells called sieve tube cells, individual sieve tube cells are separated by perforated walls(sieve plates)

Question 21

Reasons for sieve tube cells living with reduced quantities of cytoplasm, no nucleus and presence of sieve plates

Answer 21

Sieve tube cells must be living as translocation is active process sieve plates with reduced cytoplasm means resistance to flow of food substances is reduced

Question 22

Reasons for companion cells containing many mitochondria

Answer 22

Perform many genetic and metabolic functions of sieve tube cells, keeping them alive. Mitochondria provide energy needed by sieve tube cells for translocation, used to load organic compounds at source

Question 23

Why is translocation active process

Answer 23

Phloem must be able to transport substances in either direction as links parts of plant that need supply of sucrose and amino acids to other parts with a surplus.

Question 24

Why is sucrose most prevalent solute in phloem

Answer 24

Does not readily metabolise directly in respiration during transport and makes good transport form of carbohydrates

Question 25

Structure of chloroplast

Answer 25

Double membrane, stroma is dense fluid in chloroplast, interconnected membranous sacs called thylakoids separate chlorophyll and stroma.

Question 26

Why are chlorophyll green

Answer 26

Absorbs light in violent blue and red region of visible light spectrum and reflects green light

Question 27

Function of chlorophyll

Answer 27

Traps light energy and converts it into ATP for the formation of glucose and subsequent uses

Question 28

Define photosynthesis

Answer 28

Photosynthesis is the process in which light energy absorbed by chlorophyll is converted into ATP. The ATP is used to synthesise glucose from water and carbon dioxide, water and carbon dioxide are raw materials for photosynthesis. Oxygen released during the process.

Question 29

What happens in light dependent stage

Answer 29

Light energy is absorbed by chlorophyll and converted into ATP, light energy used to spilt water molecules into oxygen and hydrogen ions, known as photolysis. 12 molecules of water are spilt to yield 6 molecules of oxygen and 24 hydrogen ions, oxygen released via stomata

Question 30

What happens in light independent stage

Answer 30

Hydrogen ions released during photolysis used to reduce carbon dioxide to glucose, ATP needed for process comes from light-dependent stage, 24 hydrogen ions reduce 6 molecules of CO2 to form one molecule of glucose

Question 31

Similarity between light-dependent and light-independent stages

Answer 31

Enzymes are needed to catalyse reactions in both stages

Question 32

Difference of light-dependent stage and light-independent stage(site in chloroplast)

Answer 32

LDS occurs in thylakoid while LIS occurs in stroma.

Question 33

Difference of light-independent stage and light-independent stage(requirements)

Answer 33

Light energy, water and chlorophyll are required in LDS while CO2, chemical energy and H+ are necessary in LIS

Question 34

Difference of light-independent stage and light-independent stage(energy)

Answer 34

Light absorbed by chlorophyll and converted to chemical energy in LDS while energy in LIS is obtained from LDS

Question 35

Difference of light-independent stage and light-independent stage(reactions)

Answer 35

Photolysis-light energy used to spilt water molecules into oxygen and hydrogen ions in LDS while reduction-hydrogen ions from photolysis reduce CO2 to form glucose in LIS

Question 36

Difference of light-dependent stage and light-independent stage(products formed)

Answer 36

Products of LDS are H+, O2 and ATP while in LIS are glucose and water

Question 37

Uses of glucose in plant

Answer 37

Used in respiration to produce ATP, form cellulose cell wall, converted into sucrose for transport, converted into triglycerides and lipids for storage and synthesis of cell membranes, conversion of glucose to starch and vice versa, reacts with nitrates and mineral salts to form amino acids in leaves, form proteins for cellular materials

Question 38

3 Importance of photosynthesis

Answer 38

Makes chemical energy available to animals and other organisms, removes carbon dioxide and provides oxygen, stored in fossil fuels

Question 39

Effect of temperature on photosynthesis

Answer 39

Photosynthesis is dependent on temperature as it is catalysed by enzymes, temp ^ kinetic energy ^ increases frequency of effective collision between enzymes and substrates, ^ rate of photosynthesis. Approach optimum temp, rate reaches max. Increase beyond enzyme opt temp, rate of photosynthesis decreases till it stops as enzymes are denatured

Question 40

Effect of carbon dioxide concentration on rate of photosynthesis

Answer 40

^ in CO2 conc ^ rate of photosynthesis up to certain point, beyond point conc of CO2 increases rate of photosynthesis remains constant - other limiting factor normally impt as atmospheric CO2 remains constant at about 0.03%

Question 41

Effect of light intensity on rate of photosynthesis

Answer 41

^ in light intensity ^ rate of photosynthesis up to certain point, beyond point light intensity increases rate of photosynthesis remains constant - other limiting factor

Question 42

Define compensation point

Answer 42

Point where rate of photosynthesis equals rate of respiration no net intake or output of carbon dioxide and oxygen, glucose produced by pho. exactly compensates for glucose broken down by respiration

Question 43

Why is water not limiting factor

Answer 43

Less than 1% of water taken up is used for photosynthesis, however can affect indirectly by closing stomata, limits intake of CO2

Question 44

Describe intake of CO2

Answer 44

Photosynthesis causes CO2 in leaf to be used up, CO2 conc in leaf becomes lower than atmo, diffuses in from surrounding air through stomata into air spaces in leaf, mesophyll cells covered by thin film of water so CO2 can dissolve in it, then dissolved CO2 diffuses into mesophyll cell

Question 45

Describe movement of water via roots

Answer 45

Root hair cell grows between soil particles, close contact with soil solution surrounding them, cell sap in root hair cell is relatively conc. with sugars and mineral salts, lower water potential than soil solution and water enters root hair cell by osmosis. Entry of water dilutes sap and now has higher water potential than neighbouring cell, movement by osmosis, moves cell by cell by osmosis till it reaches xylem

Question 46

Adaptation of root hair cell for absorption of water by osmosis

Answer 46

Long and narrow extensions to increase SA:V ratio, increase rate of absorption of mineral salts and water, cell sap lower water potential than soil solution, water will continuously enter root hair cell by osmosis

Question 47

Adaptation of root hair cell for absorption of mineral salts by active transport and facilitated diffusion

Answer 47

Root hair cell contains mitochondria to provide energy for active transport of mineral salts into the cell

Question 48

Define transpiration

Answer 48

Loss of water vapour from the leaves through the stomata

Question 49

How does root pressure help in transportation of water molecules

Answer 49

Respiring cells around xylem vessels use active transport to pump mineral salts into vessels, lowering water potential in xylem vessels and causing water to move into xylem vessels by osmosis

Question 50

How does capillary action help in transportation of water molecules

Answer 50

Water molecules are polar, partial negative charge on oxygen atom in one water molecule attracts hydrogen atom in neighbouring molecule(cohesion) and water is attracted to hydrophilic parts of walls of xylem(adhesion), as a result of cohesion and adhesion water can be pulled in continuous stream

Question 51

Describe transpiration pull

Answer 51

Water evaporates from film of moisture surrounding mesophyll cells into the intercellular air space. Water vapour diffuses out of leaf via stomata via transpiration. As water leaves mesophyll cells to replenish film of moisture, water potential of cell decreases, water moves from neighbouring cells to these mesophyll cells by osmosis. The neighbouring cells then draw water from cells deeper inside of leaf. These cells draw water from xylem. This results in transpiration pull, a suction force which pulls the whole column of water up the xylem

Question 52

What is the importance of transpiration

Answer 52

Creates transpiration pull which draws water and mineral salts from roots to stem and leaves. Transpiration pull supplies water to mesophyll cell in the leaves for photosynthesis, to all cells for metabolic processes, keeps cells turgid so leaves can spread out widely to trap sunlight for photosynthesis and keeps plant upright. Transpiration removes latent heat which cools the plant which prevents it from being scorched

Question 53

How does high humidity of air surrounding leaf affect rate of transpiration

Answer 53

Higher humidity indicates the presence of a lot of water vapour in the air surrounding the leaf. This decreases water vapour concentration gradient. As such, water vapour diffuses out at a lower rate, leading to lower transpiration rate

Question 54

How does wind speed increase the rate of transpiration

Answer 54

Higher wind speed indicates that the water vapour in the air surrounding the leaf is blown away. This increases the water vapour concentration gradient. As such, water vapour diffuses out at a higher rate, leading to higher transpiration rate.

Question 55

How does higher temperature increases the rate of transpiration

Answer 55

Higher temperature increases rate of evaporation, increasing concentration of water vapour in intercellular air spaces. This increases the water vapour concentration gradient. As such, water vapour diffuses out at a higher rate, leading to higher transpiration rate. However at very high temperatures, stomata will close to prevent excessive transpiration

Question 56

When does wilting occur

Answer 56

Wilting occurs when rate of transpiration exceeds the rate of absorption at the roots

Question 57

What is the disadvantage of wilting

Answer 57

When the plants wilt, the leaves droop and less leaf surface is exposed to the sun and thus the rate of photosynthesis decreases

Question 58

What is the advantage of wilting

Answer 58

When the leaves fold up, surface area exposed to sunlight is reduced. This causes guard cells to become flaccid and stomata to close. Transpiration is thus reduced