Chapter 4 Organising Plants

Question 1

What is organisation like in plants?

Answer 1

• Cells are the basic units of life
• Groups of the same type of cells work together to form tissues
• Groups of tissues work together to form organs
• The root, stem and leaves form a plant organ system that transports substances in and around plants
• The whole plant is an organism

Question 2

List 4 plant organs.

Answer 2

Flowers, stems, leaves, roots.

Question 3

Flowers are plant organs. What is the function of flowers in plants?

Answer 3

Flowers attract pollinators so are involved in reproduction.

Question 4

Stems are plant organs.What is the function of stems in plants.

Answer 4

Stems support the plant. They contain thickened material called lignin and vessels for transport of nutrients in plants

Question 5

Leaves are plant organs. What is the function of leaves?

Answer 5

Leaves contain the pigment chlorophyll in chloroplasts. This is where photosynthesis takes place.

Question 6

Roots are plant organs. What is the function of roots?

Answer 6

Roots anchor plants in the soil and absorb and store nutrients.

Question 7

Where is meristematic tissue found in plants?

Answer 7

Meristematic tissue is found at the tips of roots and shoots and around the vascular tissue in stems.

Question 8

What are meristems?

Answer 8

Groups of undifferentiated stem cells that divide to produce all the different types of cells that make up a plant

Question 9

How long are plants capable of producing new tissue?

Answer 9

Unlike animal cells, plants can keep producing new tissue throughout their life.

Question 10

What can meristematic tissue be used for?

Answer 10

Cloning the plant to make many genetically identical plants.

Question 11

Why might a plant be cloned?

Answer 11

To make many copies of plants with desirable characteristics like disease resistance.
To protect rare plants from extinction.

Question 12

Give 2 ways rare plants can be protected from extinction?

Answer 12

1- They can be cloned
2- Their seeds can be stored in seed banks.

Question 13

Describe what happens at the apical meristem.

Answer 13

The apical meristem causes primary growth i.e. lengthening of the plant. It occurs at the tips of roots and shoots and produces new leaves and flowers.

Question 14

Describe what happens at lateral meristems:

Answer 14

Lateral meristems cause secondary growth i.e. widening of the plant. This occurs at the cambium and produces bark on trees.

Question 15

Draw a diagram to show the layers in a leaf.

Answer 15

Diagram:

Question 16

What is the function of the waxy cuticle?

Answer 16

The waxy cuticle is water resistant and reduces water loss from evaporation.

Question 17

What is the function of the upper epidermis?

Answer 17

It is thin and transparent to allow light to pass through.
It has no chloroplasts stopping it from blocking light.
It prevents water loss by evaporation.
Any damage to the outer layer may not damage photosynthesising cells.

Question 18

What is the function of the palisade mesophyll layer of cells?

Answer 18

They are regular shaped cells packed with chloroplasts.
80% of photosynthesis takes place here.
They are positioned in a row for the maximum absorption of light for photosynthesis.

Question 19

What is the function of the spongy mesophyll?

Answer 19

Spongy mesophyll cells are irregularly shaped to increase the surface area for gas exchange. Gases get passed between the air spaces, spongy mesophyll and palisade mesophyll. There are air spaces between the cells. Although there are some chloroplasts, only 20% of photosynthesis takes place here.

Question 20

What is the function of the lower epidermis?

Answer 20

The lower epidermis contains guard cells and stomata.

Question 21

What is the function of guard cells?

Answer 21

Guard cells gain water to swell and open the stomata. This controls gas exchange and water loss of the plant.

Question 22

What are stomata and what is their function?

Answer 22

Stomata are the pores created when guard cells change shape to open. They can open and close to allow gas exchange and control water loss of the plant within the environment.

Question 23

What adaptation do guard cells have?

Answer 23

The inner cell wall is thicker to cause the cell to curve to make a hole.

Question 24

List the layers in a leaf from top to bottom.

Answer 24

Waxy cuticle
Upper epidermis
Palisade mesophyll
Spongy mesophyll
Lower epidermis

Question 25

Give 6 uses for water in plants.

Answer 25

1 - Water is necessary for photosynthesis
2 - To maintain cell turgidity for structure and growth
3 - Helps in germination of seeds
4 - Helps in transport of nutrients and minerals from soil to plants
5 - Water is an essential nutrient for plants and comprises 95% of a plants tissue
6 - Transpiration from leaves stops plants from overheating

Question 26

What is the function of root hair cells?

Answer 26

Root hair cells allow uptake of water and mineral ions
Water is absorbed by osmosis.
Minerals (nitrate ions) are transported into the cells by active transport.

Question 27

How are root hair cells adapted to absorb water and minerals?

Answer 27

1 - They have a large surface area with a projection/root hair.
2 - They have thin cellulose walls to reduce the distance for transport.
3 - They have many mitochondria to provide energy for active transport.
4 - They have a large permanent vacuole to hold water.

Question 28

What is the function of xylem?

Answer 28

Xylem tissue transports water and mineral ions from the roots to the stems and leaves.

Question 29

Describe 4 adaptations of xylem to make it ideal at transport of water and dissolved minerals.

Answer 29

1 - Xylem is made of elongated dead cells arranged end to end to form continuous vessels (tubes)
2 - They contain no cytoplasm
3 - They have tough walls containing a woody material called lignin that builds up in spirals in cell walls.
4 - The contents and end walls break down to form a hollow centre.

Question 30

What is the function of phloem?

Answer 30

Phloem tissue transports dissolved sugars and amino acids from the leaves to the rest of the plant for immediate use or storage.

Question 31

What is translocation?

Answer 31

The movement of food molecules through xylem is called translocation.

Question 32

Why is translocation important?

Answer 32

Translocation is important as sugar is made in the leaves via photosynthesis (source) and needs to move location to be used for either respiration or storage (sink)

Question 33

Give 4 adaptations of phloem.

Answer 33

1 - Living phloem cells are arranged end to end.
2 - The cell walls between phloem cells break down to form perforated sieve plates. These allow water carrying dissolved food (sugars and amino acids) to move freely along the tubes from one phloem cell to the next through pores in the end walls
3 - Each phloem cell has a companion cell (which contains a nucleus and mitochondria) that keep them alive. The mitochondria of the companion cells transfer the energy needed for translocation to occur
4 - Phloem cells have lost most of their internal structure – e.g. no vacuole or nucleus. This helps to reduce any resistance during translocation and allows efficient movement of substances.

Question 34

Where are xylem and phloem vessels found in stems?

Answer 34

The vascular bundles containing xylem and phloem are arranged near the edge of the stem, with the phloem on the outside and the xylem on the inside of the vascular bundle.

Question 35

Where are xylem and phloem vessels found in leaves?

Answer 35

In leaves the vascular bundles are located among the spongy mesophyll with phloem nearer lower surface.

Question 36

What is transpiration?

Answer 36

The loss of water from leaves by evaporation.

Question 37

What is the transpiration stream?

Answer 37

The flow of water through a plant, from the roots to the leaves, in the xylem vessels. Water will eventually be lost by evaporation out of the stomata.

Question 38

How does water move through a plant (transpiration stream)?

Answer 38

1 - Root hair cells have lots of mitochondria for releasing energy for the uptake of mineral ions.
2 - Root hair cells have a large surface area for rapid water uptake.
3 - Water enters root hairs by osmosis.
4 -Water moves across the root one cell at a time.
5 - Water enters the xylem of the stem.
6 - Water moves up the xylem in the stem.
7 - Water leaves the xylem and enters the leaf cells by osmosis.
8 - Water moves across the leaf one cell at a time by osmosis.
9 - Some water is used in the cells for photosynthesis.
10 - The remaining water evaporates into the air spaces of the spongy mesophyll.
11 - In the air spaces the humidity is now high.
12 - From the air spaces water diffuses out of the stomata and evaporates out of the underside of the leaf.

Question 39

What happens in the transpiration stream?

Answer 39

1 - Water moves through the plant from the roots up to the leaves.
2 - When the guard cells are open, water evaporates out of the leaf via the stomata.
3 - This creates a shortage of water in the leaf, so water is drawn up from the roots, via the xylem to replace it.
4 - Water molecules inside the xylem cells are strongly attracted to each other. There is strong cohesion between the molecules because of hydrogen bonding. A continuous column of water is therefore pulled up the stem.
5 - More water is drawn into the roots via osmosis to replace water lost inside the roots. 6 - This is a constant cycle called the transpiration stream.

Question 40

What is cohesion?

Answer 40

Water molecules are held together by hydrogen bonds and act as a column which is why water molecules ‘stick together’ when travelling up the xylem.

Question 41

What are potometers used for?

Answer 41

Potometers measure the uptake of water by plants in different conditions. The movement of the air bubble in the tube shows how much water is taken up.

Question 42

How is a potometer used to measure the uptake of water to measure the rate of transpiration?

Answer 42

1 - Fill a beaker with water.
2 - Place a capillary tube in the beaker of water and attach it to the bottom of a test tube.
3 - Place a plant in the test tube sealed with an air tight bung.
4 - Add a ruler beneath the capillary tube.
5 - Inside the capillary tube there is an air bubble - water from the test tube is absorbed through xylem and then evaporates from stomata.
6 - Use a ruler to measure the distance moved by an air bubble over a set time.

Question 43

How accurate is a potometer at measuring transpiration rate?

Answer 43

It measures water uptake, not the water lost, as some of the water will be used in photosynthesis so it isn’t very accurate.

Question 44

Why is water uptake not the same as transpiration uptake?

Answer 44

It is only a rough gauge as some water taken up by the roots is used in photosynthesis (5-10%).

Question 45

Describe how bright light affects the rate of transpiration.

Answer 45

In bright light transpiration increases.

Question 46

Explain why light affects the rate of transpiration:

Answer 46

The stomata (openings in the leaf) open wider to allow more CO2 into the leaf for photosynthesis.

Question 47

Describe how temperature affects the rate of transpiration.

Answer 47

Transpiration is faster in higher temperatures.

Question 48

Explain why temperature affects the rate of transpiration:

Answer 48

Evaporation and diffusion are faster at higher temperatures.

Question 49

Describe how wind affects the rate of transpiration.

Answer 49

Transpiration is faster in windy conditions.

Question 50

Explain why wind affects the rate of transpiration.

Answer 50

Water vapour is removed quickly by air movement, speeding up diffusion of more water vapour out of the leaf.

Question 51

Describe how humidity affects the rate of transpiration.

Answer 51

Transpiration is slower in humid conditions.

Question 52

Explain why humidity affects the rate of transpiration.

Answer 52

Diffusion of water vapour out of the leaf slows down if the leaf is already surrounded by moist air.

Question 53

What is the disadvantage to having a large number of stomata per mm squared on a leaf?

Answer 53

This will result in a high rate of transpiration. Lots of water vapour evaporates from the surface of the leaf so the plant may wilt and possibly die.

Question 54

Why would very little water be lost if grease blocked stomata on the lower surface?

Answer 54

Stomata are found on the lower surface of the leaf. Grease blocks the stomata so water vapour could no longer evaporate out of the stomata.

Question 55

Why might stomata be called a ‘necessary evil’?

Answer 55

Stomata need to open to let carbon dioxide in for photosynthesis but it does allow for water to be lost by transpiration and if too much water is lost it could cause the plant to wilt.