y3.2: plant nutrition 🌻

Question 1

what is the definition of photosynthesis?

Answer 1

photosynthesis is the process in which light energy absorbed by chlorophyll and converted into chemical energy. water and carbon dioxide are the raw materials used to synthesise glucose and oxygen is released as a by-product

Question 2

structures of chloroplast

Answer 2

• stroma (chloroplast cytoplasm)
• thylakoid (they look like cells)
• granum (many thylakoids)

Question 3

word equation for photosynthesis

Answer 3

water + carbon dioxide –> (chlorophyll and sunlight) oxygen + glucose + water

Question 4

chemical equation of photosynthesis

Answer 4

12H2O + 6CO2 –> C6H12O6 + 6O2 + 6H2O

Question 5

describe the location and process of light-dependent stage in photosynthesis

Answer 5

• occurs in the thylakoid
• light energy is absorbed by chlorophyll and converted into ATP
• light energy is also used in the photolysis of water: 12 molecules of H2O are split to yield 6 molecules of O2 and 24 H+ ions
• oxygen is released out of the leaf via stomata

Question 6

describe the location and process of light-independent stage in photosynthesis

Answer 6

• occurs in the stroma
• hydrogen ions released from photolysis is used to reduce carbon dioxide to glucose. the energy needed for this is obtained from light-dependent stage
• 24 hydrogen ions are used to reduce 6 molecules of carbon dioxide to form 1 molecule of glucose

Question 7

how is glucose transported to the rest of the plant and why?

Answer 7

glucose is converted into sucrose to be transported by the phloem to prevent glucose from being used up by plant cells along the way

Question 8

factors affecting rate of photosynthesis

Answer 8

1) light intensity
2) carbon dioxide concentration
3) temperature

Question 9

effects of light intensity on rate of photosynthesis

Answer 9

• as light intensity increases, rate of photosynthesis increases until it reaches a plateau
• higher light intensity results in more H+ ions produced, allowing more formation of enzyme-substrate complex
• at plateau, rate of photosynthesis is limited by another factor

Question 10

what is the compensation point?

Answer 10

the point where the rate of photosynthesis equals the rate of respiration (x intercept on the oxygen output graph)

Question 11

effect of carbon dioxide concentration on rate of photosynthesis

Answer 11

• as carbon dioxide concentration increases, rate of photosynthesis increases until it reaches a plateau

Question 12

effect of temperature on rate of photosynthesis

Answer 12

• enzymes explanation because photosynthesis is a reaction catalysed by enzymes

Question 13

importance of photosynthesis

Answer 13

1) removes carbon dioxide and provides oxygen
2) give other organism access to chemical energy
3) stores energy in fossil fuels

Question 14

structures in a leaf top to bottom (🌱 = chloroplast present)

Answer 14

• cuticle
• upper and lower epidermis
• palisade mesophyll 🌱🌱
• spongy mesophyll 🌱
• vascular bundle (xylem and phloem)
• intercellular air space
• guard cells 🌱 (to form stoma)

Question 15

how do guard cells open the stoma in the day?

Answer 15

• in the day, guard cells photosynthesise
• chemical energy is used to pump potassium ions into the guard cell from the neighbouring epidermal cells, concentration of K+ in guard cells increases and water potential in guard cell decreases
• water from the neighbouring cells move into the guard cells by osmosis
• guard cells swell and become turgid
• due to difference in thickness in cell wall , one side expands more than the other and the stoma opens

Question 16

how to guard cells close the stoma at night?

Answer 16

• at night, potassium ions move out of the cell via diffusion
• water potential in guard cells increases
• water moves from guard cells into neighbouring cells by osmosis
• guard cells become flaccid and stoma closes

Question 17

describe the path of CO2 in the leaf

Answer 17

• due to photosynthesis, carbon dioxide is used up in the leaf -> carbon dioxide concentration is lower in the leaf than surroundings -> carbon dioxide moves into the leaf via diffusion into the air spaces in the leaf
• carbon dioxide dissolves into the thin film of moisture outside mesophyll cells and diffuses into mesophyll cells

Question 18

experiment shit go look at book

Answer 18

(but basically measure oxygen produced or iodine test for presence)