Topic 6: Plant Structures and Thier Functions

Question 1

write the word equation and balanced symbol equation for photosynthesis

Answer 1

Question 2

what happens for photosynthesis

Answer 2

photosynthetic organisms use energy from the sun to make glucose

Question 3

what is the glucose produced in photosynthesis used for

Answer 3

to make larger, complex molecules that the plants or algae need to grow

• this makes up the organism’s biomass

Question 4

define biomass

Answer 4

the mass of lving material

Question 5

describe what happens with a plants biomass

Answer 5

energy stored in the organism’s biomass then works its way through the food chain as animals eat them and each other.

Question 6

explain what stage of the food chain are photosynthetic organisms

Answer 6

producers
as the energy stored in the organisms biomass then works its way through the food chain as animals eat them and each other so photosynthetic organisms are the main producers of food

Question 7

inside which cell structure does photosynthesis occur

Answer 7

chloroplasts

Question 8

why does photosynthesis occur in chloroplasts

Answer 8

they contain chlorophyll which absorbs light

energy is transferred to the chloroplasts by light

Question 9

what type of a reaction is photosynthesis

Answer 9

endothermic

Question 10

describe the protocol for the practical : Investigate the effect if light intensity on the rate of photosynthesis

Answer 10

• the apparatus is set up according to the diagram
• the gas syringe should be empty to start with. Sodium hydrogencarbonate may be added to the water to make sure the plant has enough carbon dioxide (sodium hydrocarbon ate releases carbon dioxide in solution)
• a source of white light is placed at a specific distace from the pondweed
• the pondweed is left to photosynthesise for a set amount of time
• as it photosynthesises, the oxygen released will collect in the gas syringe. this allows you to accurately measure the volume of oxygen produced
• the whole experiment is repeated with the light source at different distances from the pondweed. the rate of oxygen production at each distance can then be calculated (volume of gas produced / time taken)
• for this experiment, many variables tha could effect the results should be controlled e.g. temperature by putting conical flask in a water bath, carbon dioxide concentration by adding s set amount of sodium hydrogencarbonate to set volume of water.

Question 11

how can you easily investigate the effect of light intensity on the rate of photosynthesis

Answer 11

using an aquatic (lives in water) plant like pondweed.

Question 12

what are the limiting factors of photosynthesis

Answer 12

light intensity, carbon dioxide concentration and temperature

Question 13

explain how light is a limiting factor for photosynthesis

Answer 13

• At first, as the light level is raised, the rate of photosynthesis increases steadily (the rate is directly proportional to light intensity)-
  But this is only true up to a certain point.
• Beyond that, it won’t make any difference — it’ll be either the temperature or the CO, level which is the limiting factor.

Question 14

how can you investigate effects of light intensity oh photosynthesis in the practical

Answer 14

by moving a lamp closer or further away from your plant

Question 15

describe the relationship between light intesnity and distance from the lamp

Answer 15

they are inversely proportional to each other

e.g. as distance increases, the light intensity decreases

Question 16

what is the inverse square law for distance and light intensity

Answer 16

light intensity decreases in proportion to the square of the distance

Question 17

explain how carbon dioxide concentration is a limiting factor for photosynthesis

Answer 17

• increasing the CO2, concentration increases the rate of photosynthesis up to a point. After this the graph plateaus, showing that CO2, is no longer the limiting factor.
  3) As long as light and CO, are in plentiful supply then the factor limiting photosynthesis must be temperature.

Question 18

explain how temperature is a limiting factor for photosynthesis

Answer 18

• if the temperature is the limiting factor it’s because it’s too low — the enzymes needed for photosynthesis work more slowly at low temperatures.
• But if the plant gets too hot, the enzymes it needs for photosynthesis and its other reactions will be denatured
• This happens at about 45 °C

Question 19

explain how the structure of the root hair cells is adapted to absorb water and mineral ions

Answer 19

• the cells on the surface of plant roots grow into ‘hairs’ which stick out in the soil
• each branch of a root will be covered in millions of the microscopic hairs
• this gives the plant a large surface area for absorbing water and mineral ions from the soil
• the concentration of mineral ions is usually higher in the root hair cells than in the soil around them, so mineral ions are absorbed by active transport.
• water is absorbed by osmosis

Question 20

how are phloem tubes adapted to tranport food in the plant

Answer 20

• phloem tubes are made of columns of elongated living cells with small pores in the end walls to allow stuff to flow through
• they transport food substances (mainly sucrose) made in the leaves to the rest of the plant for immediate use e.g. in growing regions or for storage
• this process is called translocation and it requires energy from respiration.
• transport gows in both directions

Question 21

how are xylem tubes adapted to transport water up the plant

Answer 21

• Xylem tubes are made of dead cells joined end to end with no end walls between them and a hole down the middle.
• They’re strengthened with a material called lignin.
• They carry water and mineral ions from the roots to the stem and leaves.
• The movement of water from the roots, through the xylem and out of the leaves is called the transpiration

Question 22

explain how water and mineral ions are transported through the plant by transpiration

Answer 22

• Transpiration is caused by the evaporation and diffusion of water from a plants surface. Most transpiration happens at the leaves.
• The loss of water creates a slight shortage of water in the leaf, and so more water is drawn up from the rest of the plant through the xylem vessels to replace it.
• This in turn means more water is drawn up from the roots, and so there’s a constant transpiration stream of water through the plant.
• The transpiration stream carries mineral ions that are dissolved in the water along with it.

Question 23

describe how sucrose is transported around the plant by translocation

Answer 23

• sucrose is translocated (transported) in the sieve tubes in the phloem tissue.
• the large central channel in each sieve cell is connected to its neighbours by holes, through which sucrose solution flows.
• companion cells actively pump sucrose into or out of the sieve cells that form the sieve tubes. as sucrose is pumped into sieve tubes, the increased pressure causes the sucrose solution to flow up to growing shoots or down to storage organs

Question 24

what is the function of stomata

Answer 24

stomata are microscopic pores in a leaf which allow carbon dioxide to diffuse into a leaf and water vapour to diffuse out.

Question 25

what is the structure of stomata

Answer 25

they are opened and closed by guard cells - In light, water flows into guard cells making them rigid - this opens the stoma. At night, water flows out of the guard cells, making the stoma shut

Question 26

what factors affects the transpiration rate

Answer 26

light intensity
temperature
air flow

Question 27

explain how light intensity affects transpiration rate

Answer 27

• the brighter the light, the greater the transpiration rate.
  stomata begin to close as it gets darker.
  photosynthesis cannot happen in the dark so they dont need to be open to let CO2 in.
  when the stomata are closed, very little water can escape

Question 28

explain how temperature effects transpiration rate

Answer 28

• the warmer it is, the faster transpiration happens.
• when its warm the water particles have more energy to evaporate and diffuse out of the stomata

Question 29

explain how air flow effects transpiration rate

Answer 29

• the better the air flow around the leaf e.g. a stronger wind, the greater the transpiration rate
• if air flow around the leaf is poor, the water vapour just surrounds the leaf and doesn’t move away.
• this means there is a high concentration of water particles outside the leaf as well as inside it, so diffusion doesn’t happen as quickly
• if there is good air flow, the water vapour is swept away, maintaining a low concentration of water in the air outside the leaf. Diffusion then happens quickly, from an area of higher concentration to an area of lower concentration

Question 30

describe the practical on how you can estimate the transpiration rate

Answer 30

• use aparatus called a potometer to estimate transpiration rate
• it measures water uptake by a plant
• it is assuming that water uptake by the plant is directly related to water loss from the leaves (transpiration)

protocol:
- set up the apparatus in the digram, and then record the starting position of the air bubble
- start a stopwatch and record the distance moved by the bubble per unit time e.g. per hour
- calculate the speed of air bubble movement gives an estimate of the transpiration rate

Question 31

how to estimate the rate of transpiration from the practical

Answer 31

distance moved / time taken

Question 32

what else can a potometer be used to estimate

Answer 32

light intensity
temperature
air flow

ONLY CHANGE ONE VARIABLE AT A TIME AND CONTROL THE REST

Question 33

label diagram of the structure of the typical leaf

Answer 33

Question 34

explain how leaves are adapted to their function of photosynthesis

Answer 34

• broad : so large surface area exposed to light, which is needed for photosynthesis
• paleside layer has lots of chloroplasts: near the top of the leaf so can absorb the most light
• transparent upper epidermis: so light can pass through to the paleside layer
• xylem and phloem form a network of vascular bundles: provide leaf with water for photosynthesis and take away glucose produced. also helps support the structure
• waxy cuticle cover epridermal tissues: helps reduce water loss by evaporation
• lower epidermis has lots of stomata which let CO2 diffuse directly into leaf for efficient gas exchange
• spongy mesophyll tissue contains air spaces which increase the rate of diffusion of gases into and out of the leaf’s cells

Question 35

how are plants living in deserts (like cacti) adapted

Answer 35

• small leaves/ spines instead of leaves: this reduces the surface area for water loss by evaporation. spines help to stop animals eating the plant to get water
• curled leaves/ hairs on surface of leaves: reduces air flow close to the leaf, trapping water vapoiur near the surface and reducing diffusion from the leaf to the air.
• thick waxy cuticles: to reduce water loss by evaporation
• thick, fleshy stem: stores water
• fewer stomata or stomata that only open at night: to reduce water loss by evaporation
• stomata sunken in pits: this makes the stomata lower than th surface of the leaf, which reduces air flow close to the stomata. this reduces water loss in the same way as curled leaves or hairs.

Question 36

what is the role of auxins

Answer 36

plant hormones which control growth at the tips of shoots and roots

Question 37

what does auxin do in the shoot of the plant

Answer 37

stimulates gorwth

Question 38

what does auxin do in the root of the plant

Answer 38

inhibit growth

Question 39

what is it called when plant growth responds to light

Answer 39

phototropism

Question 40

what is the growth response of a plant to gravity called

Answer 40

gravitropism

Question 41

explain how plant shoots are positively phototropic (grow towards light)

Answer 41

• when a shoot tip is exposed to light, it accumulates more auxin on the shaded side than on the light side
• this makes the cells elongate faster on the shaded side so the shoot bends towards the light

Question 42

how does shoots being positively phototrophic enables growth

Answer 42

• by bending towards the light the shoot will be able to absorb more light for photosynthesis which enables the plant to gorw

Question 43

why are shoots growing completely in the dark tall and spindly

Answer 43

• the auxin in the tips stimulates elongation on all sides
• a taller shoot has a better chance of finding light

Question 44

explain how shoots are negatively gravitropic (grow away from gravity)

Answer 44

• when a shoot is growing sideways, gravity causes an uequal distribution of auxin in the tip, with more auxin on the lower side
• this causes cell elongation on the lower side so the shoot bends upwards

Question 45

explain how roots are positively gravitropic

Answer 45

• a root growing sideways has more auxin on the lower side
• auxin inhibits cell elongation on the lower side so cells on the top elonate more and the root bends downwards

Question 46

explain how roots are negatively phototrophic

Answer 46

• if a root starts being exposed to some light, more auxin accumulates on the shaded side
• the auxin inhibits cell elongation on the shaded side, so the root bends downwards, back into the ground

Question 47

describe a practical to investigate plant growth responses

Answer 47

• put some cress seeds in a Petri dish lined with moist filter paper
• surround perti dish with black card and cut a hol in one side of the card only
• shine a light into the box through the hole
• leave your cress seeds alone for one week until you can observe their repsonse - you should find the seedlings grow towards the light. You can even measure the angle they are gorwing at

Question 48

what are some ways in which plant hormones have commercial uses

Answer 48

• as selective weedkillers
• growing from cuttings with rooting powder
• controlling flower and fruit formation
• producing seedless fruit
• controlling ripening of fruits
• controlling seed germination

Question 49

explain how plant hormans have the use of selective weedkillers

Answer 49

1) Most weeds growing in fields of crops or in a lawn are broad-leaved, in contrast to grasses and cereals which have very narrow leaves.
2) Selective weekillers have been developed from auxins, which only affect the broad-leaved plants.
3) They totally disrupt their normal growth patterns, which soon kills them, whilst leaving the grass and crops untouched

Question 50

explain how plant hormans have the use of growing from cuttings wih rooting powder

Answer 50

1) A cutting is part of a plant that has been cut off it, like the end of a branch with a few leaves on it.
2) Normally, if you stick cuttings in the soil they won’t grow, but if you add rooting powder, which contains auxins, they will produce roots rapidly and start growing as new plants.
3) This enables growers to produce lots of clones (exact copies) of a really good plant very quickly

Question 51

explain how plant hormans have the use of contorlling flower and fruit formation

Answer 51

1) Gibberellins are plant hormones that stimulate seed germination (growth of a seed into a plant), stem growth and flowering. They can be used to make plants flower earlier than they would usually do so, or under conditions in which they wouldn’t usually flower (e.g. when it’s warmer than usual).
2) They can also be used to reduce flower formation, which can improve fruit quality. (Fruit grows from pollinated flowers, see below.) E.g. apricot trees often produce too many flowers. This causes too many fruits to form — the tree can’t support them all and they grow quite small. Fewer flowers means fewer fruits, which are able to grow nice and big.

Question 52

explain how plant hormans have the use of producing seedless fruit

Answer 52

1) Fruit (with seeds in the middle) normally only grows on flowering plants which have been pollinated by insects. If the flower doesn’t get pollinated, the fruit and seeds don’t grow.
2) If plant hormones such as gibberellins are applied to the unpollinated flowers of some types of plant, the fruit will grow but the seeds won’t. Some seedless citrus fruits can be grown this way.

Question 53

explain how plant hormans have the use of controlling the ripening of fruits

Answer 53

1) The ripening of fruits can be controlled either while they are still on the plant, or during transport to the shops. This allows the fruit to be picked while it’s still unripe (and therefore firmer and less easily damaged).
2) A ripening hormone called ethene is then added and the fruit will ripen on the way to the supermarket and be perfect just as it reaches the shelves.

Question 54

explain how plant hormans have the use of controlling seed germination

Answer 54

1) Lots of seeds won’t perminate until they’ve been through certain conditions (e.g. a period of cold or of dryness).
2) Seeds can be treated with siberellins to make them germinate at times of year that they wouldhit normally. It also helps to make sure all the seeds in a batch germinate at the same time.