plant organisation Flashcards
bbc bitesize
1
Q
active transport
definition
A
The transport of molecules against their concentration gradient from a region of low concentration to a region of high concentration.
2
Q
companion cells
definition
A
Cells that help the phloem to transport substances by providing energy.
3
Q
diffuse
definition
A
When particles spread out from a region of higher concentration to a region of lower concentration.
4
Q
epidermal cells
definition
A
Cells of the epidermis, the outer covering layer of an organism.
5
Q
eyepiece
definition
A
The eyepiece, or ocular, is the lens at the top of a compound microscope. It has a longer focal length than the objective lens and magnifies the image produced by the objective.
6
Q
field of view
definition
A
The area seen when looking through a microscope.
7
Q
flaccid
definition
A
Lacking turgor. Lacking in stiffness or strength. Soft and floppy.
8
Q
graticule
definition
A
A glass or plastic disc fitted into the eyepiece of a microscope. The graticule has a scale ruled on it and is used to estimate the size of a specimen when viewed with a microscope.
9
Q
hydrogen bonding
definition
A
The strongest type of van der Waals force that arises through a dipole-dipole attraction when hydrogen atoms are covalently bonded to highly electronegative nitrogen, oxygen or fluorine atoms.
10
Q
lignin
definition
A
Carbohydrate material lining the xylem vessels providing strength and support.
11
Q
mitochondria
definition
A
Structures in the cytoplasm of all cells where aerobic respiration takes place (singular is mitochondrion).
12
Q
nuclei
definition
A
The nucleus controls what happens inside the cell. Chromosomes are structures found in the nucleus of most cells. The plural of nucleus is nuclei.
13
Q
osmosis
definition
A
The movement of water molecules across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration.
14
Q
palisade mesophyll
definition
A
Plant tissue containing closely packed cells in the upper layer of a leaf.
15
Q
phloem
definition
A
The tissue in plants that transports the products of photosynthesis, including sugars and amino acids.
16
Q
photosynthesis
definition
A
A chemical process used by plants to make glucose and oxygen from carbon dioxide and water, using light energy. Oxygen is produced as a by-product of photosynthesis. Algae subsumed within plants and some bacteria are also photosynthetic.
17
Q
representative sample
definition
A
A representative sample is one that accurately represents the whole of the group.
18
Q
root hair cell
definition
A
A specialised cell that increases the surface area of the root epidermis to improve the uptake of water and minerals.
19
Q
respiration
definition
A
The chemical change that takes place inside living cells, which uses glucose and oxygen to release the energy that organisms need to live. Carbon dioxide is a by-product of respiration.
20
Q
sieve tube
definition
A
Cells that have no nuclei and are connected to each other by their cytoplasm.
21
Q
spongy mesophyll
definition
A
The plant tissue in a leaf which has loosely packed cells and air spaces between them to allow gas exchange.
22
Q
stomata
definition
A
Tiny holes in the epidermis (skin) of a leaf. They control gas exchange by opening and closing and are involved in loss of water from leaves. Singular is stoma.
23
Q
sucrose
definition
A
A disaccharide made from glucose and fructose. It is used as table sugar.
24
Q
translocation
definition
A
The transport of dissolved material within a plant.
25
transpiration
| definition
The loss of water from leaves by evaporation through the stomata.
26
tuber
| definition
A swollen, fleshy underground stem of a plant, such as the potato, bearing buds from which new plant shoots arise.
27
turgid
| definition
Having turgor - enlarged and swollen with water.
28
xylem vessels
| definition
Narrow, hollow, dead tubes with lignin, responsible for the transport of water and minerals in plants.
29
What are leaves adapted for?
Leaves are adapted for photosynthesis and gaseous exchange.
30
How are leaves adapted for photosynthesis and gaseous exchange?
They are adapted for photosynthesis by having a large surface area, and contain openings, called stomata to allow carbon dioxide into the leaf and oxygen out. Although these design features are good for photosynthesis, they can result in the leaf losing a lot of water. The cells inside the leaf have water on their surface. Some of this water evaporates, and the water vapour can then escape from inside the leaf.
31
Transpiration
When water evaporates from the leaves, resulting in more water being drawn up from the roots, it is called transpiration.
32
How are leaves adapted to reduce water loss?
To reduce water loss the leaf is coated in a waxy cuticle to stop the water vapour escaping through the epidermis. Leaves usually have fewer stomata on their top surface to reduce this water loss.
33
How are leaves adapted for photosynthesis?
Leaves enable photosynthesis to occur. Photosynthesis is the process by which leaves absorb light and carbon dioxide to produce glucose (food) for plants to grow. Leaves are adapted to perform their function, eg they have a large surface area to absorb sunlight.
34
What are the 2 different types of transport tissues in plants and what do they do?
Plants have two different types of 'transport' tissue, xylem and phloem. These specialised tissues move substances in and around the plant.
35
Functions of leaves.
| Photosynthesis
The function of a leaf is photosynthesis - to absorb light and carbon dioxide to produce glucose (food). The equation for photosynthesis is:
carbon dioxide and water → glucose and oxygen
36
Functions of leaves.
| Gas exchange in leaves.
Leaves are also involved in gas exchange. Carbon dioxide enters the leaf and oxygen and water vapour leave the plant through the stomata. Leaves are adapted in several ways to help them perform their functions.
37
Name the purpose of the adaptation large surface area of leaves.
To absorb more light
38
Name the purpose of the adaptation thin of leaves.
Short distance for carbon dioxide to diffuse into leaf cells
39
Name the purpose of the adaptation chlorophyll of leaves.
Absorbs sunlight to transfer energy into chemicals
40
Name the purpose of the adaptation network of veins of leaves.
To support the leaf and transport water, mineral ions and sucrose (sugar)
41
Name the purpose of the adaptation stomata of leaves.
Allow carbon dioxide to diffuse into the leaf and oxygen to diffuse out
42
Functions of tissues of the leaf
| Name the purpose of the adaptation epidermis is thin and transparent
To allow more light to reach the palisade cells
43
Functions of tissues of the leaf
| Name the purpose of the adaptation thin cuticle made of wax
To protect the leaf from infection and prevent water loss without blocking out light
44
Functions of tissues of the leaf
| Name the purpose of the adaptation palisade cell layer at top of leaf
To absorb more light and increase the rate of photosynthesis
45
Functions of tissues of the leaf
| Name the purpose of the adaptation spongy layer
Air spaces allow gases to diffuse through the leaf
46
Functions of tissues of the leaf
| Name the purpose of the adaptation palisade cells contain many chloroplasts
To absorb all the available light
47
Gas exchange in plants
When a plant is carrying out photosynthesis carbon dioxide needs to move from the air into the leaf. It does this by diffusing through small pores called stomata.
At the same time oxygen moves out of the leaf through the stomata. This movement of gases in opposite directions is called gas exchange.
Water vapour also diffuses out of the stomata. The stomata are surrounded by guard cells, which control their opening and closing. Cells in the leaf are loosely packed.
48
Plants absorbing light energy
Light absorption happens in the palisade mesophyll tissue of the leaf. Palisade cells are column shaped and packed with many chloroplasts. They are arranged closely together so that a lot of light energy can be absorbed.
49
What does xylem move?
xylem moves water and mineral ions from the roots to the leaves
50
What does phloem do?
phloem moves food substances such as sucrose (sugar) and amino acids from leaves to the rest of the plant. This movement of food is called translocation.
51
Root hair cells
Plants absorb water from the soil by osmosis. They absorb mineral ions by active transport, against the concentration gradient. Root hair cells are adapted for taking up water and mineral ions by having a large surface area to increase the rate of absorption. They also contain lots of mitochondria, which release energy from glucose during respiration in order to provide the energy needed for active transport.
52
Root hair cell
| The absorbed water is transported through the roots to the rest of the plant where it is used for different purposes:
- it is a reactant used in photosynthesis
- it supports leaves and shoots by keeping the cells rigid
- it cools the leaves by evaporation
- it transports dissolved minerals around the plant
53
What are stomata?
Stomata are tiny holes found in the underside of leaves. They control water loss and gas exchange by opening and closing. They allow water vapour and oxygen out of the leaf and carbon dioxide into the leaf.
54
Stomata
Plants growing in drier conditions tend to have small numbers of tiny stomata and only on their lower leaf surface, to save water loss. Most plants regulate the size of stomata with guard cells. Each stoma is surrounded by a pair of sausage-shaped guard cells. In bright light the guard cells take in water by osmosis and become plump and turgid. In low light the guard cells lose water and become flaccid, causing the stomata to close. They would normally only close in the dark when no carbon dioxide is needed for photosynthesis. Guard cells are adapted to their function by allowing gas exchange and controlling water loss within the leaf.
55
Size of stomata
The size of the stomatal opening is used by the plant to control the rate of transpiration and therefore limit the levels of water loss from the leaf. This helps to stop the plant from wilting.
56
Xylem consists of dead cells. The cells that make up the xylem are adapted to their function:
- They lose their end walls so the xylem forms a continuous, hollow tube.
- They become strengthened by a substance called lignin. Lignin gives strength and support to the plant. We call lignified cells wood.
57
The phloem moves food substances that the plant has produced by photosynthesis to where they are needed for processes such as:
- growing parts of the plant for immediate use
- storage organs such as bulbs and tubers
- developing seeds
58
Transport in the phloem
Transport in the phloem is therefore both up and down the stem. Sucrose is the transport sugar in the phloem. Transport of substances in the phloem is called translocation. Translocation requires energy as it is an active process.
59
Phloem consists of living cells. The cells that make up the phloem are adapted to their function:
- Sieve tubes - specialised for transport and have no nuclei. Each sieve tube has a perforated end so its cytoplasm connects one cell to the next. Sucrose and amino acids are translocated within the living cytoplasm of the sieve tubes.
- Companion cells - transport of substances in the phloem requires energy. One or more companion cells attached to each sieve tube provide this energy. A sieve tube is completely dependent on its companion cell(s).
60
Type of transport in xylem
Physical process
61
Type of transport in phloem
Requires energy
62
Substances transported in xylem
Water and minerals
63
Substances transported in phloem
Products of photosynthesis; includes sucrose and amino acids dissolved in water
64
Direction of transport in xylem
Upwards from roots to leaves
65
Direction of transport in phloem.
Upwards and downwards
66
Transpiration
When the plant opens its stomata to let in carbon dioxide, water on the surface of the cells of the spongy mesophyll and palisade mesophyll evaporates and diffuses out of the leaf. This process is called transpiration.
67
Xylem
water molecules
hydrogen bonding
Water molecules inside the xylem cells are strongly attracted to other water molecules. There is strong cohesion between the molecules because of hydrogen bonding. A continuous column of water is therefore pulled up the stem in the transpiration stream by evaporation from the leaves.
68
Transpiration is an unavoidable consequence of photosynthesis - only five per cent of the water taken up by the plant is used for photosynthesis - but does have its purposes:
- provides the water for photosynthesis
- transports mineral ions
- cools the leaf as water evaporates
- provides water that keeps the cells turgid, which supports herbaceous plants
69
Water uptake and transport across the root
Root hairs are single-celled extensions of epidermal cells in the root. They grow between soil particles and absorb water and minerals from the soil.
Water enters the root hair cells by osmosis. This happens because soil water has a higher water potential than the cytoplasm of the root hair cell. Minerals enter by active transport.
70
The rate of transpiration is affected by several factors. These include:
- temperature
- humidity
- air movement
- light intensity
71
What is the change in factor that increases transpiration rate for the factor temperature
increase
72
What is the change in factor that increases transpiration rate for the factor humidity
decrease
73
What is the change in factor that increases transpiration rate for the factor air movement
increase
74
What is the change in factor that increases transpiration rate for the factor light intensity
increase
75
Explain how the factor temperature increases the transpiration rate
Increases molecular movement so that: more water molecules evaporate from cell surfaces; the rate of diffusion of water molecules from the leaf is increased
76
Explain how the factor humidity increases the transpiration rate
Reduces the concentration of water molecules outside the leaf; diffusion of water from the leaf increases
77
Explain how the factor air movement increases the transpiration rate
Removes water vapour from leaf surfaces; more water diffuses from the leaf because a high concentration gradient is maintained
78
Explain how the factor light intensity increases the transpiration rate
Increases the rate of photosynthesis; stomata open so that water diffuses out of the leaf
79
What conditions will decrease the rate of transpiration?
Decrease in temperature, increase in humidity, no or reduced air movement and low light intensity.
80
What is a simple method for investigating water loss from plant leaves?
A simple method for investigating water loss from plant leaves is to measure their change in mass over a period of time.
81
Various factors that affect water loss from the leaf can be investigated using this method, for instance:
- air movement - direct a fan on the leaves
- temperature
- obstructing the stomata, eg. with petroleum jelly
82
A simple method for investigating water loss from plant leaves is to measure their change in mass over a period of time.
Explain this method step by step.
1) Remove a number of leaves from a bush or tree.
2) Find the mass of each leaf.
3) Suspend each leaf from a piece of wire or string.
4) After a set period of time, re-measure the mass.
83
Water loss through the stomata
Water is lost through open stomata. Scientists sometimes count all the stomata on a leaf surface, but usually, there are too many to count. In these instances, they take a sample. This must be a representative sample - it must give a true picture of the numbers of stomata on the leaf.
84
To be representative of the whole leaf, the representative sample must:
- include a sufficient number of counts - not just one or two - of stomata over different parts of the slide
- must be random, and not select areas where there are many or few stomata
85
Water loss through the stomata
sample
counting stomata
A number of random counts of stomata should be made with a microscope.
Count the number of stomata in the field of view. Then move the slide slightly and count the number of stomata in a different field of view.
Make at least five random counts, then calculate a mean.
Using this method, and a calibrated eyepiece graticule, you could estimate the number of stomata per unit area (mm2).
86
Investigating transpiration
How to measure the uptake of water
The uptake of water can be measured using a potometer. Under normal circumstances, the rate of water uptake gives a measure of the rate of transpiration.
A simple potometer is a piece of capillary tubing to which a plant has been connected. The water uptake is measured by recording the time taken for a bubble in the tube to move a set distance.
87
Measuring water uptake - Potometers
Investigating transpiration
step by step
1) The potometer is filed with water
2) A shoot is cut from a plant
3) The end of the shoot is cut under water to ensure the xylem remains water-filled and prevents air locks.
4) The shoot is inserted into the rubber tubing at the end of the potometer
5) The potometer is raised so that a bubble of air is taken up.
6) The potometer is lowered into the water. The distance travelled by the air bubble is recorded over a period of time.
88
Investigating factors that affect the rate of transpiration
Insufficient water affects the yields of crops. Different factors affect transpiration and therefore water uptake. They can be investigated using a potometer.
89
Laboratory experiments are designed to simulate conditions a plant may encounter such as:
- air movement
- coatings on leaves that block stomata
- high light intensity
- high temperature
90
Laboratory experiments are designed to simulate conditions a plant may encounter such as air movement.
Explain when this is encountered by the plant and how the condition is produced in the laboratory.
When encountered by plant: Windy conditions
How the condition is produced in the laboratory: Fan
91
Laboratory experiments are designed to simulate conditions a plant may encounter such as coatings on leaves that block stomata.
Explain when this is encountered by the plant and how the condition is produced in the laboratory.
When encountered by plant: Airborne pollution; horticultural use on cuttings and Christmas trees
How the condition is produced in the laboratory: Smear leaf surface(s) with petroleum jelly
92
Laboratory experiments are designed to simulate conditions a plant may encounter such as High light intensity.
Explain when this is encountered by the plant and how the condition is produced in the laboratory.
When encountered by plant: Sunny climates; artificial lighting in greenhouses
How the condition is produced in the laboratory: Artificial lighting
93
Laboratory experiments are designed to simulate conditions a plant may encounter such as High temperature.
Explain when this is encountered by the plant and how the condition is produced in the laboratory.
When encountered by plant: Warm and hot climates
How the condition is produced in the laboratory: Heater or greenhouse
94
When investigating the effect of light intensity on water uptake, what are the control variables?
Temperature, no air movement or draughts. It is also important to use the same species of plant, and shoots with a similar leaf surface if different plant shoots are used.
95
Under which conditions is the rate of transpiration greatest?
At high temperatures.
96
Scientists use sampling and counting techniques to investigate the distribution of stomata on leaves. They count stomata to investigate:
- their numbers, density and distribution on upper and lower surfaces
- numbers that are open and closed at any time
- adaptations of plants to environmental conditions, eg desert and water plants
- effects of changing conditions such as increased carbon dioxide concentrations from climate change
97
Give 2 methods (step by step) by which stomata can be counted.
Method 1
1) Put a small drop of water on a microscope slide.
2) Hold the leaf with the surface you want to examine uppermost.
3) Tear the leaf at an angle so as to reveal part of the epidermis.
4) Place the leaf on the microscope slide and examine.
Method 2
1) Paint the surface of the leaf with clear nail varnish.
2) Allow to dry.
3) Peel off the nail varnish with forceps.
4) Place on a dry microscope slide and examine
98
Recording the distribution
The density of stomata on a leaf is recorded per unit area, usually the number per sq mm.
A microscope is calibrated so that its field of view is known.
99
Adaptations of plants to extreme environments
| Cacti are well adapted for survival in the desert. They have:
- Stems that can store water.
- Widespread or very deep root systems that can collect water from a large area or from very deep underground.
- Spines which are modified leaves. These minimise the surface area and so reduce water loss. The spines also protect the cacti from animals that might eat them.
- Very thick, waxy cuticle to reduce water loss by evaporation.
- Reduced number of stomata to reduce water loss by transpiration.
100
Which tissue in the leaf absorbs the most light for photosynthesis?
Palisade mesophyll
101
Which tissue in the leaf is adapted for efficient gas exchange?
Spongy mesophyll
102
Which tissue transports water and minerals from the root to the leaves?
Xylem
103
Which tissue transports sugars from the leaves to other parts of the plant including roots for storage?
Phloem
104
Translocation is the movement of which substance?
Sucrose
105
Which cells control the stomata?
A pair of guard cells surround each stoma and when they are turgid, the stoma will be open.
106
What sort of process is translocation?
active process
107
What is the process which causes guard cells to become turgid?
Osmosis
108
Which of these describes the stomata of a desert plant?
Reduced in number and mainly closed
