Chapter 12 - Nutrition and Transport in Flowering Plants

Question 1

What are the external structures of the leaf?

Answer 1

1) Network of veins
2) Lead blade/Lamina
3) Leaf arrangement
4) Leaf stalk

Question 2

Describe the network of veins

Answer 2

• Transports water and M.S. from roots to cells in leaf blade
• Transports manufactured food from cells in leaf blade to other parts of the plant

Question 3

Describe the leaf blade

Answer 3

• Large flat surface provides greater surface area to volume ratio for leaf to trap the maximum amount of light for photosynthesis
• Large thin leaf blade allow rapid diffusion of carbon dioxide to inner cells due to shorter diffusion distance

Question 4

Describe the leaf arrangement

Answer 4

• Organised around the stem in a regular pattern
• Grow in pairs/singly in an alternate arrangement
• Prevents the leaves from blocking each other so each can obtain sufficient amount of sunlight

Question 5

Leaf stalk

Answer 5

• Holds the leaf blade away from stem to obtain sufficient light and air
• Some leaves (e.g. grass, maize) do not have a leaf stalk, but have long leaf blades

Question 6

What are the internal structures of the leaf

Answer 6

1) Upper epidermis
2) Mesophyll (palisade & spongy)
3) Lower epidermis
4) Cuticle
5) Stomatal pore (stomata)
6) Guard cell

Question 7

Describe the upper epidermis (characteristics + function)

Answer 7

1) Single uppermost layer of cells - protects inner layer of cells
2) Covered by a layer of waxy cuticle - reduces evaporation of water from leaf & prevents entry of disease causing microbes
3) Cells do not contain chloroplasts and are transparent - allows light to penetrate into the inner layers

Question 8

Describe the palisade mesophyll

Answer 8

1) One or two layers of long cylindrical cells closely packed - vertical arrangement exposes many cells to light
2) Contains numerous/most chloroplasts - being nearer to the top surface, has cells that receive more amount of light energy. Hence most photosynthesis takes place in this region

Question 9

Describe the spongy mesophyll

Answer 9

1) Irregularly shaped, loosely arranged cells with many intercellular air spaces in between - air spaces allow rapid diffusion of carbon dioxide and oxygen in and out of the mesophyll cells
2) Cells are surrounded by a thin film of moisture - gases entering the cells can dissolve in it
3) Chloroplasts present (fewer than in palisade) - photosynthesis takes place in cells
4) Contains vascular bundle as transport tissues - Xylem transports water and M.S. and phloem transports manufactured food

Question 10

Describe the lower epidermis

Answer 10

1) Beneath the mesophyll, lowest layer of closely packed cells - protects the inner tissues
2) Covered by waxy cuticle - slows down loss of water
3) Has guard cells and stomata. Guard cells that surround the stomata - regulate opening and closing of stomata for diffusion of carbon dioxide and oxygen in and out of the leaf

Question 11

Describe the cuticle

Answer 11

The cells are covered by an outer layer of cuticle, which reduces water loss through epidermal cells

Question 12

Describe the stomatal pore (stoma)

Answer 12

The lower epidermis contains many small openings called stomata (singular: stoma)

Question 13

Describe the guard cell

Answer 13

1) Surround stomata, bean shaped, uneven thickness of walls
2) Contains chloroplasts, only epidermal cell that photosynthesise
3) Controls size of stomata to regulate the exchange of gases/transpiration between the leaf and the environment by opening and closing the stoma

Question 14

How do guard cells open the stoma?

Answer 14

In sunlight:
1) Guard cells photosynthesize, producing glucose
2) This lowers the water potential in the cell sap
3) Water from the surrounding epidermal cells enter the guard cell by osmosis, making the cells turgid
4) The thicker inner wall causes the cells to curve, opening the stoma

Question 15

Why do stomata close on hot sunny days?

Answer 15

To prevent water loss:
1) Excess evaporation causes guard cells to lose water
2) They become flaccid and less curved
3) The stoma closes, reducing transpiration to conserve water

Question 16

What happens to stomata at night?

Answer 16

1) Photosynthesis stops (no sunlight = no glucose production)
2) Glucose is used up or converted into starch, which does not dissolve easily in water
3) This increases the water potential inside the guard cells
4) Water leaves the guard cells by osmosis into surrounding cells
5) Guard cells become flaccid and less curved → stomata close

Question 17

How is the leaf adapted for photosysnthesis?

Answer 17

1) Waxy cuticle on upper and lower epidermis
2) Stomata present in epidermal layers
3) Chloroplasts containing chlorophyll in mesophyll cells
4) More chloroplasts in upper palisade tissue
5) Interconnecting system of air spaces in spongy mesophyll
6) Veins connecting xylem and phloem situated close to mesophyll cells

Question 18

Describe the adaptation of waxy cuticle on upper and lower epidermis

Answer 18

Waxy cuticle on upper and lower epidermis - reduces water loss from evaporation, transparent for light to enter

Question 19

Describe the adaptation of stomata present in epidermal layers

Answer 19

Stomata present in epidermal layers - Stomata open in presence of light, allowing carbon dioxide to diffuse in and oxygen to diffuse out

Question 20

Describe the adaptation of chloroplasts containing chlorophyll in mesophyll cells

Answer 20

Chloroplasts containing chlrophyll in all mesophyll cells - Chlorophyll absorbs energy from light and ransfers it to chemical stores of energy in glucose molecules

Question 21

Describe the adaptation of more chloroplasts in upper palisade tissue

Answer 21

More chloroplasts in upper palisade tissue - more light absorbed near upper leaf surface

Question 22

Describe the adaptation of interconnecting system of air spaces in the spongy mesophyll

Answer 22

Interconnecting system of air spaces in spongy mesophyll - allow rapid diffusion of carbon dioxide and oxygen in and out of the mesophyll cells

Question 23

Describe the adaptation of veins containing xylem and phloem situated lose to mesophyll cells

Answer 23

Veins containing xylem and phloem situated near mesophyll cells - xylem transports water and M.S. to mesophyll cells, phloem transports sucrose away from leaf

Question 24

How does carbon dioxide enter the leaf?

Answer 24

1) Through the lower epidermis of the leaf that contains numerous stomata
2) Due to photosynthesis, concentration of carbon dioxide decreases as it is used up rapidly
3) Creates a carbon dioxide concentration gradient between the atmosphere and cell, carbon dioxide diffuses from the atmosphere to the intercellular air spaces
4) Moist surface of the mesophyll cells allow carbon dioxide to dissolve in it so and then diffuse into cells

Question 25

How does water and dissolved mineral salts enter the leaf?

Answer 25

1) Water and dissolved M.S. absorbed through the roots, travels up the stem and enters leaf though leaf stalk 2) Tiny tubes in leaf veins contains xylem that carries water throughout the leaf blade 3) Once water is out of xylem, it moves from one mesophyll cell to the other by osmosis

Question 26

What are the 2 types of transport tissues?

Answer 26

Xylem --> Transports water & M.S from roots the stem to leaves + provides mechanical support for plant Phloem --> Transports manufactured food (sucrose and amino acids) from leaves to all parts of the plant

Question 27

Describe the xylem tissue

Answer 27

- Xylem tissue consists of xylem vessels which are long, continuous and hollow tubes made up of dead cells --> reduces resistance to water flowing through xylem - Inner walls (cellulose cell walls) are strengthened by deposits of a substance called lignin in the form of rings/spiral/whole vessel except for tiny holes called pits --> provides mechanical support to plant - Xylem vessels conduct water and M.S. in one direction, upwards from the roots to the rest of the plant

Question 28

Describe the phloem

Answer 28

- Consists of sieve tubes formed by sieve tube cells and companion cells - STC are elongated with thin layer of cytoplasm, stack on top of each other to form ST - ST transports manufactured food up and down the plant - Companion cells are narrow, thin walled cells that have numerous mitochondria, cytoplasm and a nucleus - CC carries out metabolic processes and provide nutrients to keep the STC alive and help them transport food - Mitochondria provides energy needed to move the sugar from the mesophyll cells into the ST by active transport - ST has sieve plates with holds allowing food to move through rapidly

Question 29

Within a vascular bundle, which tube is closer inside and which is closer outside?

Answer 29

Xylem --> Closer inside Phloem --> Closer outside Tissue (Cambium) between them

Question 30

What is the stem covered by?

Answer 30

Layer of cells (epidermis). The epidermal cells are protected by a waxy, waterproof cuticle that reduces evaporation from stem

Question 31

Where are vascular bundles found?

Answer 31

Along the spongy mesophyll

Question 32

Within vascular tissues in leaves, where is the xylem and phloem closer to?

Answer 32

Xylem --> Upper surface of leaf Phloem --> Lower surface of leaf

Question 33

Describe the vascular tissues in roots

Answer 33

- The epidermis of the root is the outermost layer of cells with root hairs - Each hair is long and narrow extension growing out the epidermal cell (increases SA:V, increased rate of absorption of water and M.S.)

Question 34

What is photosynthesis?

Answer 34

Photosynthesis is the process by which green plants synthesise carbohydrates in carbon dioxide and water and in the presence of light, glucose is manufactured and oxygen is released

Question 35

What absorbs energy during photosynthesis?

Answer 35

The chlorophyll absorbs energy from light and transfers it to chemical stores of energy in carbohydrates which are synthesised from water and carbon dioxide. Oxygen is released as a by-product

Question 36

What is the word equation for photosynsthesis?

Answer 36

Carbon dioxide + Water ⟶ (light + chlorophyll) ⟶ Glucose + Oxygen

Question 37

What is the balanced chemical equation for photosynthesis?

Answer 37

6CO₂ + 6H₂O ⟶ (light + chlorophyll) ⟶ C₆H₁₂O₆ + 6O₂

Question 38

What happens to excess glucose in the leaf?

Answer 38

Converted to starch for storage

Question 39

What are the limiting factors in photosynthesis and why are they LF?

Answer 39

1) Light intensity 2) Carbon dioxide concentration 3) Temperature They can limit the rate of photosynsthesis when they are absent in sufficient quantities

Question 40

What is a limiting factor?

Answer 40

Any factor that directly affects the rate of a chemical reaction. Rate of reaction increases if value of LF increases

Question 41

When does a LF become a non LF?

Answer 41

When the LF is no longer affecting the rate of a chemical reaction even when it increases further, its not an LF

Question 42

Why does rate of photosynthesis increase when light intensity increase?

Answer 42

When more light is supplied to the plant, the amount of nergy for photosyntheiss increases causing the rate to increase as well

Question 43

When a certain point is reached, why does light intensity not affect the rate of photosynthesis?

Answer 43

At this point, light intensity is no longer the LF since rate of photosynsthesis remains constant regardless of light intensity. Carbon dioxide or temperature could be a LF

Question 44

Why does rate of photosynthesis when carbon dioxide amount increase?

Answer 44

More carbon dioide is available for photosynsthesis, more glucose can be produced in the plant increasing the rat eof photosynthesis

Question 45

When a certain point is reached, why does carbon dioxide not affect the rat eof photosynthesis?

Answer 45

The concentration of carbon dioxide is no longer a LF because its increase has no effect on the rate of photosynthesis. A LF could be light intensity or temperature

Question 46

What is the relationship between temperature and rate of photosynthesis?

Answer 46

As temperature in plants increases towards optimum, the rate increases. Thus, temperature is a LF until it reaches optimum. If temperature increases beyond optimum, rate decreases as the enzymes involved in photosynthesis are denatured at high temperatures

Question 47

What are the 5 uses of glucose?

Answer 47

1) Used immediately in leaves 2) Conversion between glucose and starch 3) Converting to sucrose 4) Converted to amino acids in leaves 5) Forming fats

Question 48

Explain how glucose is used immediately in leaves

Answer 48

- For cellular respiration to provide energy for cellular activities - Forming cellulose

Question 49

Explain how glucose is used in conversion betqween glucose and starch

Answer 49

- In daylight excess glucose is covnerted into starch for storage - In darkness, starch is converted back to glucose

Question 50

Explain how glucose is used in converting to sucrose

Answer 50

Sucrose is: - Transported to other parts of the pant/storage organs (e.g. seeds, root tubers) - Converted to other forms of storage compounds as storage organs - Converted back to glucose by enzymes for respiration - A component of nectar in flowers to attract insects for pollination

Question 51

Explain how glucose is used converting to amino acids in leaves

Answer 51

- Amino acids form proteins that are needed to make protoplasm in leaves - Amino acids transported to other parts of the plant for synthesis of new protoplasm and for storage as proteins

Question 52

Explain how glucose is used in forming fats

Answer 52

- For storage _ For synthesis of new protoplasm - Used in cellular respiration

Question 53

What are the essential conditions for photosynthesis to occur?

Answer 53

1) Light 2) Carbon dioxide 3) Chlorophyll 4) Suitable temperature 5) Sufficient water

Question 54

Why is photosynthesis important?

Answer 54

1) Making chemical energy available to animals and other organisms 2) Photosynthesis removes carbon dioxide and provides oxygen 3) Energy stored in fossil fuels come from photosynthesis

Question 55

Explain how making chemical energy available to animals and other organisms is important

Answer 55

- During photosynthesis, chlorophyll absorbs energy from light and transfers it to chemical stores of energy in carbohydrates - Carbohydrates are converted into fats, proteins, other organic compounds - These become food for other organisms - Plants are the producers in the food chain and all organisms obtain chemical energy from them directly/indirectly

Question 56

Explain how photosynthesis removes carbon dioxide and provides oxygen is important

Answer 56

- Photosynthesis removes carbon dioxide from the air and releases oxygen - Oxygen allows living organisms to carry out respiration to release energy for cell activities - Maintains a constant level of carbon dioxide and oxygen in the atmosphere

Question 57

Explain how energy stored in fossil fuels is important

Answer 57

- Energy in fossil fuels like coal, oil, gas come form the sun, captured through photosynthesis - Coals are formed form trees - When coal is burnt, energy in the chemical store of coal can be used to drive machinery/transfer to other energy stores

Question 58

How do you test if photosynthesis has occurred through experiments?

Answer 58

- Test for presence of starch, when photosynthesis is carried out actively, glucose forms more quickly than used up and excess glucose is converted to starch - However, starch formation may not indicate that photosynthesis has occurred, because starch can be formed in the roots or underground storage organs - Destarch (to ensure that starch is absent in leaves before experiment) and place the plant in darkness, no photosynthesis = enzymes convert starch to sucrose - Use iodine solution to test for starch (brown to blue-black) or no starch (remains brown)

Question 59

What is translocation?

Answer 59

The transport of manufactured food substances (e.g. sugars, amino acids) in plants

Question 60

What are the 3 studies that provide evidence of translocation in the phloem tissue in a plant?

Answer 60

1) 'Ringing' experiment 2) Using aphids in translocation studies 3) Using isotopes in translocation studies

Question 61

Describe the 'ringing' experiment

Answer 61

- A ring of bark with the phloem is removed from the stem of a plant - Swelling above the ring is observed - Caused by accumulation of food substances from the leaves because the food substances cannot be transported to the stem below the ring

Question 62

Describe the aphids in translocation studies experiment

Answer 62

- Aphids feed on plant juices by inserting their feeding stylet into the leaf/stem - When the aphid's body is removed, the stylet is left in the plant tissues - A liquid containing sucrose and amino acids can be observed exuding from the cut end of the stylet - The stylet is found to be inserted into the phloem sieve tube, showing that translocation of sugars and amino acids take place in phloem tissues

Question 63

Describe the isotopes in translocation studies experiment

Answer 63

- Carbon-14 is a radioactive isotope of carbon detected by an X-ray - When a leaf is exposed to carbon dioxide containing carbon-14, sugars formed will contain carbon-14 and are transported in the stem - If a section of the stem containing the carbon-14 sugars is cut and placed in an X-ray film, only the phloem tissue is darkened - Provides evidence that phloem tissue is responsible for transport of sugars

Question 64

Describe the entry of water into a plant

Answer 64

1) Absorption of water occurs in the root hairs (tubular outgrowth of root epidermal cells, an epidermal cell + root hair = root hair cell) 2) RHC is in direct contact with thin film of liquid between soil particles that contain a dilute solution of mineral salts 3) The thin film has a higher water potential than the cell sap of the RHC, creating a water potential gradient allowing water to enter the RHC by osmosis 4) The water dilutes the cell sap, increasing its water potential of the RHC next to it, causing the water to move from one RHC to the net by osmosis until it reaches the xylem vessel which carries the water up the plant

Question 65

Describe the entry of mineral salts and ions into the plant

Answer 65

- When the concentration of M.S. and ions in the soil solutions is higher than the RHC, they are absorbed in aqueous form through diffusion, down the concentration gradient - When the concentration of mineral salts and ions in the soil solution is lower than in the RHC, they are absorbed into the roots through active transport against the concentration gradient (requires energy from respiration)

Question 66

What are the adaptations of RHC to its function of absorption?

Answer 66

1) Long and narrow -> increases surface area to volume ratio to enhance the rate of absorption of water and mineral salts 2) Cell membrane preventing cell sap from leaking out -> allows cell sap to become more concentrated that soil solution as sugars, amino acids and salts are kept inside the cell. Water will enter the roots by osmosis 3) Contain many mitochondria - provides energy for active transport of mineral salts and ions into the cell

Question 67

What is the movement of water in the xylem caused by?

Answer 67

Transpirational pull, created by a process called transpiration

Question 68

What is transpiration?

Answer 68

The loss of water vapour from aerial parts of a plant, mainly the stomata

Question 69

How is transpiration pull created by transpiration?

Answer 69

- The evaporation of water from the leaves removes water from the xylem vessels - Results in a suction force (transpirational pull) which pulls the water up the vessels in vascular bundles - When water moves out the mesophyll cells, it forms a thin film of moisture over their surface, which then evaporates into the ICAS, causing the concentration of water vapour in the ICAS to increase, allowing it to diffuse out through the stomata resulting in loss of water vapour (transpiration) - Thin film of moisture is replenished by more water moving out the mesophyll cells as it evaporates, the wp of their cell sap becomes lower than the wp in the neighbouring mesophyll cells, allowing the mesophyll cells to draw water from the deeper mesophyll cells by osmosis - Deep mesophyll cells extract water from xylem vessels by osmosis producing a suction force that pulls water upwards in the vessels (transpirational pull)

Question 70

How is transpiration linked to gas exchange?

Answer 70

In daylight, stomata opens to allow carbon dioxide to diffuse into the leaf for photosynthesis. Oxygen and water vapour are more concentrated in the intercellular air spaces, so they diffuse out of the leaf through the stomata

Question 71

Why is transpiration important?

Answer 71

- Water can be transported to leaves for photosynthesis to keep cells turgid and replace water lost by the cells, turgid cells enable leaves to spread out widely and trap light for photosynthesis - Transpiration pull moves water and mineral salts up from the roots to the stems to the leaves