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R2101 Science > Leaves - Structure & Function > Flashcards

Leaves - Structure & Function Flashcards

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1
Q

What is the primary function of leaves?

A

Photosynthesis

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2
Q

What are the 7 labels on a leaf?

A

Petiole, midrib, margin, Lamina (leaf blade), stipules, veins, node.

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3
Q

What is the petiole location, characteristics and function?

A

Attaches leaf blade (laminar) to the stem. The base is attached to the stem at a node.
Is stem like.
Holds leaf in position for photosynthesis.
Conducts water and nutrients.
Attaches lamina to stem.

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4
Q

What is the lamina location, characteristics and function?

A

Expanded thin structure on either side of the midrib. Also known as leaf blade. Usually largest part of leaf.
Large surface area and many chloroplasts.
Many different shapes.
Function is to maximise photosynthesis. Facilitating water movement through transpiration from leaves that creates the pull.

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5
Q

What is the Veins location, characteristics and function?

A

Network across the leaf in DIcot.
Parallel veins in Monocot.
Main branches of the vascular system.
Patterns may be useful to identify species.
Conducts water and nutrients through vascular system to surrounding tissue.

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6
Q

What is the Midrib location, characteristics and function?

A

Single main vein central to leaf in dicots.
Extension of the petiole into the lamina.
Provides structure and rigidity.
Conducting water and nutrients through vascular system to surrounding tissue.

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7
Q

What kind of leaves do conifers or gymnosperms have?

A

Needle like or scale like leaves

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8
Q

What two types of leaves are there?

A

Simple or Compound

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9
Q

What is a simple leaf?

A

Lamina is undivided eg. Digitalis purpurea. Majority of leaves are simple.

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10
Q

What is a compound leaf?

A

The leaf blade or lamina is divided into several leaflets. Eg. Horsechesnut, Ash, Rosa rugosa ‘Alba’. Compound leaves can be classed as palmate and pinnate.

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11
Q

How to tell if a leaflet or an individual leaf?

A

A true leaf will have an auxillary bud at the base where the petiole meets the stem.
If there is no bud there, it is an individual leaflet and therefore the overall leaf is compound.

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12
Q

What is a Rachis?

A

The central axis point of a compound leaf. (not called a petiole!)

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13
Q

Name two types of compound leaf arrangement?

A

Pinnate and Palmate

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14
Q

What does a palmate leaf look like?

A

Leaflets radiating outwards from one point like fingers.

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15
Q

What does a pinnate leaf look like?

A

Leaflets held in opposite pairs on the petiole.

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16
Q

What leaf shape is a Rosa rugosa ‘Alba’.

A

Pinnate compound

Leaf composes of leaflets in rows. Can be odd (leaflet at tip) or even.

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17
Q

What leaf shape is a horse chesnut?

A

Palmate compound.

Resembles a hand.

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18
Q

What leaf vein arrangement does a monocotyledon have?

A

Parallel veins

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19
Q

What leaf vein arrangement does a dicotyledon have?

A

Reticulate veins

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20
Q

What does sessile mean?

A

No petiole - leaf is attached directly to the stem.

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21
Q

What does Peltate mean?

A

Petiole attached to centre lamina. Eg. Tropaolum majus. Or Pilea peperomioides

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22
Q

What does perfoliate mean?

A

Stem pierces the leaf - eg. Claytonia perfoliata (winter purslane)

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23
Q

What does petiolate mean?

A

Leaf is held on a petiole. eg. Abutilon ‘White King’ or Abutilon ‘Kentish belle’.

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24
Q

What are the 5 different types of leaf arrangement?

A 
Alternate
Opposite (completely rotated)
Opposite (on same plane, not rotated)
Whorled
Rosulate
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25
Q

Describe alternate leaf arrangement and an example?

A

Leaves arranged singly on alternate sides of the stem. eg. Fagus sylvatica.

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26
Q

Describe opposite leaf arrangement?

A

Opposite leaves arranged in pairs on the same plane. May be rotated.

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27
Q

Describe an opposite leaf arrangement which doesn’t have rotation?

A

Opposite leaves in pairs on the same plane. May not be rotated.

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28
Q

Describe whorled leaf arrangement and an example?

A

Leaves in groups of 3 or more attached to the stem. Fritallaria imperialis

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29
Q

Describe Rosulate leaf arrangement and an example?

A

leaves in a rosette - eg. Sempervivum tectorum

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30
Q

Example of a variegated leaf?

A

Fatsia japonica ‘Spiders Web’

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31
Q

List 10 Elements of the internal structure of a dicot leaf?

A

Cuticle, epidermis, trichlome, Palisade mesophyll, spongy mesophyll (also known as parenchyma tissue) Xylem, Phloem, Vascular bundle, Stomata, guard cells

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32
Q

Describe the Palisade mesophyll cells?

A

These are tightly packed cells that hang from the epidermis where they can receive light evenly. Parenchyma tissue.

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33
Q

Describe the spongy mesophyll cells?

A

These are loosely packed cells to allow gas and water vapour to move freely in the air spaces between cells. Parenchyma tissue.

34
Q

What are the stomata?

A

Stoma (or stomata for more than one) are the pores on the underside of the leaf and their opening and closing is controlled by the surrounding guard cells.
Stomata are part of the epidermal tissue.

35
Q

Adaptation of a leaf for storage/perrenation?

A

A bulb. There are two types.

  1. Tunicate with papery sheath - Narcissus ‘February gold’ or Tulipa ‘Queen of the Night’
  2. Scaly with no papery sheath or tunic - Lilium regale.
36
Q

Adaptation of a leaf for water storage?

A

Hylotelphium telphium.

37
Q

Adaptation of a leaf for protection?

A

Leaf spines. Description for a sharp protrusion derived from the leaf.
Berberis thunbergii ‘Atropurpurea’ (the whole leaf is a spine!)
or Cactus.

38
Q

Adaptation of leaf for climbing?

A

Tendrils - modified upper leaflets that become very thin and long.
Eg. Lathyrus odoratus

39
Q

Second Adaptation of leaf for climbing?

A

Twining petioles - modified leaf petioles that twist around oth er stems or wire trellis for anchorage so they can climb.
Eg. Clematis montana

40
Q

Adaptation of a leaf to attract pollinators?

A

Bracts - modified leaves coloured with bright coloured pigmentation. They can be confused with petals. Species with bracts tend to have small insignificant flowers.
Eg. Hydrangea arborescens ‘Annabel’
Poinsettia
Bougainvillea

41
Q

Leaves as crops?

A

Leaves - chives or lettuce Lactuca sativa.
Fleshy leaf base - leek Allium porrum
Petiole - celery or rhubarb
Large leaf bud - brussel sprouts.

42
Q

Compare a monocotyledon and a dicotyledon leaf?

A 
Monocots
Leaf shape strap like
Sheath like leaf attachment
Parallel veins
Stomata on upper and lower surface
Dicots
Leaf shape can be varied and is often broad/lobed.
Leaf attachment is a petiole.
Has reticulate vein pattern.
Stomata on lower surface.
43
Q

Definition of photosynthesis?

A

A chemical reaction which takes place in the chloroplasts in the mesophyll cells of the leaf.
Plants use energy from the sun to manufacture sugars from carbon dioxide and water giving off oxygen as a by-product.

44
Q

What is the scientific equation for photosynthesis?

A

Carbon dioxide + light energy from sun + water =

Sugars (carbohydrates/glucose/starch) + Oxygen

45
Q

Where does photosynthesis take place?

A

In the chloroplasts of the mesophyll cells of the leaves. There are more chloroplasts in the upper layer (palisade mesophyll). Often leaves are darker on the top. Leaves are food making factories!

46
Q

Can photosynthesis take place anywhere other than the leaves?

A

Also the stems, but mainly the leaves.
Palisade mesophyll cells first on the upper layer.
Then the Spongy mesophyll cells underneath to a lesser degree.

47
Q

Where does the Carbon dioxide come from?

A

Carbon dioxide enters the leaf through the plant via the Stomata when they are open by diffusion and moves from the external atmosphere through the stomata and into the mesophyll cells. Stomata are pores on the underside of the leaf, which are surrounded by 2 guard cells that control the opening and closing.

48
Q

Where does the water come from?

A

Water is taken up by the root hairs and flows up to the leaves through the petiole into the midrib and veins and then it passes into the mesophyll cells.

49
Q

Where does the light come from?

A

Light comes from the sun or could be provided by supplementary lighting in the greenhouse.

50
Q

How do the stomata work?

A

Stomata open and close depending on the turgidity of the guard cells. If the plant is suffering from lack of water the stomata will close to conserve water. If water is readily available the stomata will open and this allows carbon dioxide to enter by diffusion. This happens in daylight, as stomata close at night time to conserve water as there is no daylight to photosynthesise.

51
Q

How do the stomata pores open and close?

A

Stomata is surrounded by 2 sausage shaped guard cells. As water is lost and guard cells become flaccid they shrink and the pores close.
When guard cells have ample water they become turgid and the pores open.

52
Q

What are the two words you need to know when describing the opening and closing of stomata and the guard cells?

A

Turgid - swollen with water

Flacid - drooping or inelastic through lack of water.

53
Q

What are the 3 main limiting factors which affect the rate of photosynthesis?

A

Light
Carbon dioxide
Temperature

54
Q

What happens to plants if light levels are low?

A

Plants may over compensate by using energy to divide cells and grow and not form thick cellulose walls resulting in spindly growth or etiolation. (Plants are stretching towards the light)

55
Q

How can the grower increase light intensity/reduce etiolation?

A

In late winter use supplementary lighting.
Turn seedlings each day to prevent bending towards the light.
Keep glass of windows/greenhouse clean.
Don’t sow seeds to early in the season.

56
Q

What 3 elements of light can affect photosynthesis?

A

Intensity of light
Quality / PAR of light
Duration of light

57
Q

Describe intensity of light?

A

This is the number of photons of light hitting an area of the leaf. Highest around mid day in Summer. High in a greenhouse where the rays of light are contained and bounce around.
In winter light intensity is lower.
Light intensity is affected by cloud leaves, aspect and thickness of cuticle.

58
Q

Describe Wavelength/Quality of the light or PAR?

A

PAR = Photosynthetically active radiation.

Chlorophyll in the chloroplasts of the leaves absorbs particular wavelengths of light. This is PAR light.

59
Q

Describe duration of light?

A

Shorter days means less light and vice versa. Day length also affects flower initiation.

60
Q

How can the grower manipulate Co2 levels?

A

Provide Co2 generators in enclosed greenhouses.
Use a paraffin or gas heater which gives off Co2.
Ventilate the greenhouse.

61
Q

What is the optimum temperature for photosynthesis?

A

15-25 degrees c.
0-10 degrees - enzymes do not work efficiently. (enzymes are catalysts which assist in chemical reactions.)
Above 25 degrees the enzymes start to break down so when the temperature reaches this critical level the rate of photosynthesis will start to fail.

62
Q

What is a limiting factor?

A

Anything in short supply that will limit the rate of photosynthesis.

63
Q

What happens if you have a slow rate of photosynthesis?

A

Slower growth.

64
Q

What can you do if you don’t have enough light?

A

Use supplementary lighting.
Use a greenhouse.
Use reflective surfaces - such as foil to help increase light levels.

65
Q

Is water a limiting factor?

A

No! Although it is an ingredient in photosynthesis, it cannot be isolated as one of the main limiting factors as it is important in all aspects of plant growth.

66
Q

Can nutrients be classed as a limiting factor in photosynthesis?

A

No. As nutrients are essential for all aspects of plant growth.
It can affect the rate of photosynthesis. Chlorophyll contains Magnesium and Nitrogen and Potassium ions. Iron needed for making chlorophyll. So if any are in short supply it will affect the rate of photosynthesis.

67
Q

How can we maximise photosynthesis in the protected environment?

A

Regulate temperatures so not too high or low.
Install thermometer, heater, open vents/auto vents.
Position Greenhouse in sheltered W-E axis for maximum winter light..
Keep glass/polythene clean.
Use supplementary lighting in Winter.
Use shading to prevent temperatures soaring in summer. Or damp down floors regularly.
Use Co2 generators in commercial greenhouses which have limited air inlets.

68
Q

Summary of the pathway of water through the leaf only?

A
  1. Xylem in veins.
  2. Across leaf cell by Osmosis and diffusion flow across the mesophyll cells..
  3. Evaporates from spongy mesophyll cells into the mesophyll air spaces.
  4. Diffuse through stomata of leaf to external atmosphere.
    This is called transpiration.
69
Q

What is transpiration?

A

Evaporation of water vapour from the leaves and other plant surfaces into the atmosphere.
It is a form of diffusion.

70
Q

What 4 factors affect the rate of transpiration?

A

Relative humidity
Temperature
Wind speed
Light

71
Q

Describe Relative humidity and how it affects the rate of transpiration?

A

The difference in humidity between the inside and the outside of the leaf.
If air surrounding plant is very humid/moist - the concentration gradient between the inside and the outside of the leaf will be similar, so water won’t move by diffusion.
In contrast if it’s very dry or windy, the rate of transpiration will be quicker and the plants will potentially dry out.

72
Q

What can horticulturists do to increase/decrease RH?

A

Misting or damping down greenhouse to increase RH.
Stem cuttings covered in a plastic bag to increase humidity.
When taking cuttings spray inside of plastic bag with water, and take cuttings early in the morning before excess transpiration occurs. (stomata closed at night)
Windbreaks or shelter belts to reduce air flow and so increase humidity around plants.
Plants used as a windbreak are tolerant to strong winds and often have thick cuticles.

73
Q

How does temperature affect transpiration rate?

A

Increase in temperature leads to an increase in transpiration rate since temperature increase speeds up diffusion. Horticulturalists can use a cool fan in a glasshouse, open doors and air vents or move plants out of the sun if they’re in pots in order to reduce the rate of transpiration.

74
Q

How does wind speed affect transpiration rate?

A

Fast moving air reduces the boundary layer of still air surrounding the leaf and increases the water vapour concentration gradient between the inside and the outside of the leaf. Meaning transpiration increases.
Horticulturalists can errect a windbreak (hedge) to slow the wind.

75
Q

How does light affect transpiration rate?

A

Affects transpiration due to it’s stomata activity. At night they are usually closed. Unless specially adapted.

76
Q

3 Adaptations to minimise water loss?

A

Hairs in the leaf epidermis
Thick cuticle
Needles

77
Q

How do hairs in the leaf epidermis prevent moisture loss?

A

They trap moist air near the leaf surface which reduces the gradient between the inside and outside of the leaf. Thus reducing transpiration. Eg. Centaurea montana

78
Q

How does a thick cuticle help prevent moisture loss?

A

Thicker waxy cuticle reduces evaporation through the cuticle. Eg. Ilex aquifolium

79
Q

How do needles help prevent moisture loss?

A

Leaves (needles) have a reduced surface area which reduces the amount of area from which water can evaporate. Conifers show this. Pinus nigra.

80
Q

4 characteristics of the internal structure of a leaf which maximise photosynthesis?

A
  1. Palisade mesophyll layer is organised to maximise light reaching photosynthesising chloroplasts. Cells are closely packed together to conserve the surface area of the whole leaf. There are many chloroplasts i the palisade mesophyll cells. Most leaves are greener on the top.
  2. Epidermis is one cell thick improving light penetration to the photosynthesising cells. Palisade mesophyll.
  3. Spongy mesophyll has more air spaces for more efficient carbon dioxide and water diffusion.
  4. Thin- to reduce distance for carbon dioxide to diffuse through the leaf and to ensure light penetrates into the middle of the leaf.

R2101 Science (7 decks)

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