Topic 6 - Plants

Question 1

What is photosynthesis

Answer 1

Endothetmic reaction that uses light energy to react carbon dioxide and water to produce glucose and oxygen

Question 2

What is the word equation for photosynthesis

Answer 2

Carbon dioxide + Water -> glucose + oxygen

Question 3

What is symbol equation for photosynthesis

Answer 3

6CO₂ + 6H₂O –> C₆H₁₂O₆ + 6O₂

Question 4

What factors affect the rate of phtosynthesis

Answer 4

• Temperature
• Light Intensity
• Carbon Dioxide Concentration

Question 5

What is a limiting factor

Answer 5

A variable that limits the rate of a particular reaction

Question 6

Explain how temperature affects the rate of photosynthesis

Answer 6

• Higher temperatures provide more KE for enzymes involved in photosynthesis so rate increases as temperature rises

Question 7

Explain how light intensity affects rate of photosynthesis

Answer 7

Rate of photosynthesis is directly proportional to light intensity therefore as light intensity increases the rate of photosynthesis increases

Question 8

Why does rate of photosynthesis eventually plateau even if light intensity continues to increase

Answer 8

Another factor (such as temperature or CO₂ concentratoin) becomes limiting

Question 9

How can effect of light intensity on rate of photosynthesis on rate of photosynthesis be measured in lab (2 marks)

Answer 9

• Using light meter
• Using inverse square law where light intensity ∝ 1/distance²

Question 10

Why does rate of photosynthesis decrease as distance from light source increases

Answer 10

Light intensity is inversely proportional to square of distance from light source. Thus, as the distance increases, light intensity decreases and rate of photosynthesis decreases

Question 11

Explain how carbon dioxide concentration affects rate of photosynthesis

Answer 11

As carbon dioxide concentration increases, the rate of photosynthesis increases

Question 12

Why does rate of photosynthesis eventually plateau even if CO₂ concentration continues to increase

Answer 12

Another factor (temperature or light intensity) becomes limiting

Question 13

Which structure in plants is adapted for uptake of water and minerals

Answer 13

Root hairs

Question 14

What are adaptations of root hair cells

Answer 14

• Large surface area for fast osmosis
• Many mitochondria to release energy from respiration for active transport to mineral ions

Question 15

What is function of root hair cells

Answer 15

Absorb water through osmosis and mineral ions through active transport

Question 16

What are adaptations of Xylem cells

Answer 16

• Cells with no end walls to form hollow tubes to allow vertical water movement
• Lignin - Strength and waterproofing
• Pits to allow horizontal water movement

Question 17

What is function of xylem cells

Answer 17

Transports water and mineral ions in process known as transpiration up from roots, where they have been absorbed, to the leaves

Question 18

What are adaptations of phloem

Answer 18

• Sieve end plates that contain no nucleus and little cytoplasm to allow sugars to flow easily
• Companion cells contain dense cytoplasm, nucleus and mitochondria. They provide energy for processes in both cell types

Question 19

Describe the transpiration stream

Answer 19

• Movement of water from roots to leaves
• Water absorbed by root hair cells through osmosis
• Water travels up through xylem
• Water evaporates
• Water vapour diffuses out of leaf through stomata

Question 20

How does transipration stream transport mineral ions

Answer 20

Dissolved in water that is carried by transpiration stream

Question 21

What are stomata

Answer 21

Pores found in lower epidermis of leaf which allow gas exchange

Question 22

What factors affect rate of water uptake by plant

Answer 22

• Light intensity
• Air movement
• Temperature

Question 23

How does light intensity affect rate of transpiration

Answer 23

• High light intensity means greater number of stomata open to allow gas exchange for photosynthesis
• Rate of photosynthesis increases so more water is taken up from soil pushing water up xylem
• More water vapour diffuses out of stomata therefore rate of transpiration increases

Question 24

How does temperature affect rate of transpiration

Answer 24

• Temperature increases, water molecules have more KE so rate of diffusion increases
• Photosynthesis also increases so more water is taken up from soil, pushing water up xylem
• More water diffuses out of stomata therefore rate of transpiration increases

Question 25

How does air movement affect rate of transpiration

Answer 25

* Air movement increases, high water concentration gradient maintained between air spaces in leaf and atmosphere * Increased rate of diffusion of water molecules out of the stomata * Rate of transpiration increases

Question 26

How can rate of trabspiration be calculated using potometer

Answer 26

Rate of transpiration = distance moved by bubble / time taken

Question 27

What is role of auxins in growth of shoots in response to light

Answer 27

* Auxins moved to shaded part of plant shoot * Causing cells to elongate * Making plant bend towards light, example of positive phototropism

Question 28

What is role of auxins the growth of roots in response to light and gravity

Answer 28

* Auxins collect in large amounts on underside of root * Inhibiting cell elongation * Causing cells above to elongate faster * Causing root to grow downards in direction of gravity, example of positive gravitropiam

Question 29

Explain uses of auxins, gibberellins and ethene in commercial production of plants and fruit | 6 marks

Answer 29

**Auxins** * Used in selective weed killers * Target broad leaves plants * Kills the weeds and not narrow leaf crops * Root powder, added to the end of cutting to stimulate the growth of roots **Gibberellins** * Stimulate germination in dormant seeds * Initiate breakdown of starch by amylase * Stimulate flower formation and promotes fruit formation * Stimulate development of seedless fruits * Sprayed onto plants before pollination **Ethene** * Fruit ripening * Unripe fruit is harvested, ethene is added so fruit ripens for selling

Question 30

Compare and contrast the structure and function of xylem tissue and phloem tissue

Answer 30

**Structure** * Xylem has lignin walls for strength and waterproofing, whereas the phloem does not contain lignin * Xylem has no end walls between cells to form hollow tubes to allow vertical water movement, whereas the phloem has sieve end plates between cells * Xylem has pits to allow horizontal water movement, whereas the phloem does not have pits * Xylem is made of dead cells with no nucleus and no cytoplasm, whereas the phloem contains some living cells **Function** * Xylem transports water and mineral ions from the roots up the plant (unidirectionally) in a process known as transpiration, whereas the phloem transports sucrose from the leaves up and down the plant (bidirectionally) in a process known as translocation

Question 31

Describe the structure of the leaf and the functions of the tissues in the leaf | 6 marks

Answer 31

**Upper epidermis** * covered by a waxy cuticle, waterproof to prevent water loss and entry of pathogens * cells contain no chloroplasts -- transparent to allow light to reach the mesophyll layers below **Palisade mesophyll tissue** * made of palisade cells with many chloroplasts with chlorophyll to absorb as much light as possible for photosynthesis * below the transparent upper epidermis to receive as much light as possible for photosynthesis **Spongy mesophyll tissue** * contains cells with fewer chloroplasts than palisade mesophyll tissue * large surface area with air spaces to allow diffusion of carbon dioxide and oxygen **Lower epidermis** * contains guard cells surrounding a pore known as the stoma (plural is stomata) to -- carbon dioxide to diffuse in and oxygen to diffuse out, --water vapour to diffuse out of the leaf

Question 32

Explain the adaptations that desert plants (xerophytes) have that allow them to survive in this extreme environment | 6 marks

Answer 32

* Spines/small leaves with small surface area to prevent water loss by evaporation * Thick waxy cuticle to prevent water loss by evaporation * Few stomata/ stomata sunken in pits to prevent water loss by evaporation * Swollen stems to collect and store water

Question 33

Explain the role of auxins in the growth of shoots and roots in response to light | 6 marks

Answer 33

**shoot growth** * auxins moved to the shaded part of the plant shoot * causing cells to elongate * making the plant bend towards the light, example of positive phototropism **root growth** * auxins collect in large amounts on the underside of the root * inhibiting cell elongation * causing the cells above to elongate faster * causing the root to grow downwards in the direction of gravity, example of positive gravitropism

Question 34

Explain the uses of auxins, gibberellins and ethene in the commercial production of plants and fruits | 6 marks

Answer 34

**Auxins** * Used in selective weed killers * Target broad leaves plants * Kills the weeds and not narrow leaf crops * Root powder, added to the end of cutting to stimulate the growth of roots **Gibberellins** * Stimulate germination in dormant seeds * Initiate breakdown of starch by amylase * Stimulate flower formation and promotes fruit formation * Stimulate development of seedless fruits * Sprayed onto plants before pollination **Ethene** * Fruit ripening * Unripe fruit is harvested, ethene is added so fruit ripens for selling

Question 35

Devise an investigation to study the effect of light intensity on the rate of photosynthesis | 6 marks

Answer 35

* apparatus set up: pondweed in water in beaker * light intensity varied by changing distance of lamp from plant * counting bubbles of gas released or collecting gas and measuring volume in a syringe in a set time to calculate rate of photosynthesis * control variable: same length of pondweed, same species of pondweed, control temperature by using a water bath * repeat and calculate mean

Question 36

Devise an investigation to study the effect of light intensity on the rate of transpiration | 6 marks

Answer 36

* Apparatus set up: shoot in potometer * Light intensity varied by changing dinstance of lamp from shoot * Record distance air bubble travels in set time and calculate rate of transpiration * Control variable: same species of plant, temperature * Repeat and calculate mean