Chapter 7 - Nutrition in Plants

Question 1

What are the characteristics and functions of the lamina? [2]

Answer 1

Characteristic: Thin with a large S.A to vol. ratio [1]

Function: max. absorption of sunlight during photosynthesis + rapid diffusion of CO2 into leaf [1]

Question 2

What is the function of the petiole? [1]

Answer 2

Position leaf away from stem for max. absorption of sunlight and gaseous exchange [1]

Question 3

What are the functions of the veins? [1]

Answer 3

Transports water & minerals to leaves and food substances / sugars away from leaves [1]

Question 4

How are leaves arranged? What is the purpose? [3]

Answer 4

Arrangement: paired or alternate [1]

Purpose: Ensures leaves do not block one another from sunlight [1] each leaf receives optimum amt of sunlight [1]

Question 5

What is the upper epidermis? [1]

Answer 5

Single layer of irregular, closely packed cells covered by a waxy cuticle (NO CHLOROPLAST) [1]

Question 6

What is the function of the waxy cuticle on the upper epidermis? [3]

Answer 6

Prevents excessive water loss through evaporation [1],

Protects epidermis from disease causing microbes [1],

Transparent to allow sunlight to pass through [1]

Question 7

What is the palisade mesophyll? [1]

Answer 7

Closely packed, long, cylindrical cells containing a lot of chloroplasts for max. absorption of sunlight [1]

Question 8

What is the spongy mesophyll? [2]

Answer 8

Loosely packed, irregularly shaped cells with few chloroplasts.[1] A thin film of moisture lining cells and intercellular air spaces allow for fast gaseous exchange and photosynthesis [1]

Question 9

What is the vascular bundle? [2]

Answer 9

Lies within spongy mesophyll layer [1], contains xylem and phloem that transport substances [1]

Question 10

What is the lower epidermis? [1]

Answer 10

Single layer of irregular, closely packed cells with stomata and guard cells [1]

Question 11

What is the stomata? [1]

Answer 11

Opening controlled by guard cells and allow CO2 to enter and O2 to exit in the presence of light [1]

Question 12

What is the function of guard cells? [2]

Answer 12

Control size of stomata to regulate gaseous exchange between plant and surroundings. [1]

Help photosynthesise since they contain chloroplasts [1]

Question 13

How do the guard cells operate in sunlight to allow for CO2 intake? [3]

Answer 13

Guard cells photosynthesise and the chemical energy converted from light energy is used to pump K+ ions into guard cells from neighbouring epidermal cells [1]

K+ ions lower w.p in guard cells and allow water molecules from adjacent epidermal cells to move into guard cells by osmosis until they become turgid [1]

The thicker cell wall on the side around stomatal pore causes the swollen guard cells to become more curved and pull the stoma open. [1]

Question 14

How do the guard cells operate at night? [2]

Answer 14

K+ ions accumulated in guard cells during the day diffuses out of the guard cells, increasing the w.p in guard cells and causes water molecules to move out guard cells by osmosis. [1]

Guard cells hence become flaccid and the stoma closes, allowing plants to minimise water loss through transpiration at night, and regulate rate of diffusion and passage of gases. [1]

Question 15

How do leaves intake carbon dioxide? [4]

Answer 15

CO2 in the leaf is rapidly used up for photosynthesis in the day. [1]

The CO2 in leaf is lower than the amount of CO2 in surroundings, hence creating a diffusion gradient. [1]

CO2 diffuses from surroundings into leaf via stomata. [1]

Surfaces of mesophyll cells are covered by a thin film of water in which the CO2 will dissolve in, which then diffuses into cells. [1]

Question 16

How do leaves intake water and dissolved minerals? [2]

Answer 16

Water and dissolved minerals from roots are transported to leaves by xylems, that pass through the petioles and through the leaves, which branch throughout mesophyll layers. [1]

Once out of the vein, water and mineral salts move from cell to cell through mesophyll of the leaf by osmosis and diffusion respectively. [1]

Question 17

Define photosynthesis. [1]

Answer 17

Process by which plants convert carbon dioxide and water into sugars using sunlight as energy in the presence of chlorophyll. [1]

Question 18

What is the chemical equation for photosynthesis? [1]

Answer 18

6CO2 (g) + 6H2O (l) —-> C6H12O6 (s) + 6O2 (g) [1]

light + chlorophyll

Question 19

What happens during the light-dependent stage of photosynthesis? [3]

Answer 19

Absorption of light energy by chlorophyll [1]

Conversion of light energy absorbed to chemical energy to be used in light-independent stage [1]

Photolysis of water using light energy into hydrogen ions and oxygen atoms that combine to form O2 gas and released into the air [1]

Question 20

What happens during the light-independent stage of photosynthesis? [1]

Answer 20

Chemical energy and H+ ions produced in light stage is used to reduce CO2 to form glucose by a series of enzymatic reactions for the plant’s life processes [1]

Question 21

What is a limiting factor? [1]

Answer 21

A factor that directly affects or changes rate of reaction if its quantity or concentration is altered [1]

Question 22

What are the 3 main limiting factors of photosynthesis? [3]

Answer 22

Temperature, carbon dioxide, light intensity [1m each]

Question 23

In a graph, which part shows something is a limiting factor? Which part shows something is no longer a limiting factor? [2]

Answer 23

When the y-value increases as x-value increases [1]

When the y-value constant as x-value increases [1]

Question 24

Why does rate of photosynthesis drop drastically if temperature is increased too high? [3]

Answer 24

Photosynthesis is an enzyme-catalysed reaction, [1] so enzyme activity drops sharply at high temperatures as high temperatures break the bonds within the enzyme and changes its 3D active site, causing it to lose its original shape [1] and denaturing the enzyme. [1]

Question 25

Photosynthesis is an enzyme-catalysed reaction. State the three points to discuss when talking about enzyme reactions at any point on a graph. [3]

Answer 25

Rate of reaction / Enzyme activity
Kinetic energy + Chances of collision b/w substrate and enzyme
Enzyme-substrate complex

[1m each]