2.3 Plant tissues, organs and systems

Question 1

2.3.1 Plant tissues

Plant tissue structure: epidermal tissue

top layer

Answer 1

Epidermal tissues:
* the upper tissue layer of a leaf.
* thin and transparent - allows light to reach the photosynthesising cells in the palisade mesophyll
* with the waxy cuticle, it also protects the leaf from damage.

Question 2

2.3.1 Plant tissues

Plant tissue structure: palisade mesophyll

second layer

Answer 2

Palisade mesophyll:
* **most of the photosynthesis takes place. **
* Cells are found close together and packed full of chloroplasts - absorbs the light energy needed for photosynthesis
* at the top of the leaf - absorbs as much light energy as possible.

Question 3

2.3.1 Plant tissues

Plant tissue structures: spongy mesophyll

3rd layer

Answer 3

Spongy mesophyll:
* contains air spaces to allow gas exchange to take place.
* carbon dioxide needed for photosynthesis can circulate and diffuse into cells
* oxygen produced from photosynthesis can diffuse out of the cells and into the air spaces and will eventually diffuse out of the leaf through the stomata.

Question 4

2.3.1 Plant tissues

Plant tissue structure: xylem cell

Answer 4

Xylem carries water from the roots to the rest of the plant.

Question 5

2.3.1 Plant tissue

Plant tissue structure: phloem cells

Answer 5

Phloem vessels transport sugars from photosynthetic regions of the plant (e.g. the leaves) to other parts of the plant.

Question 6

2.3.1 Plant tissue

Plant tissue structure: phloem cells

Answer 6

Phloem vessels transport sugars from photosynthetic regions of the plant (e.g. the leaves) to other parts of the plant.

Question 7

2.3.1 Plant tissues

Plant tissue stucture: meristem tissue

Answer 7

• found at the growing tips of roots and shoots and contains stem cells (unspecialised cells, able to divide into any type of cell to form other parts of plant)
• The meristems also contain cells which are actively dividing which allows the plant to grow.

Question 8

2.3.1 Plant tissue

Plant tissue structure: stomata

Answer 8

• gaps in the leaf which control gas exchange
• allow carbon dioxide to move into leaf for photosynthesis and oxygen to leave the leaf

Question 9

2.3.1 Plant tissue

Plant tissue structure: guard cells

Answer 9

• found at either side of stomata
• responsible for opening and closing the stomata (based on light intensity)
• night: the guard cells close the stomata to prevent too much water vapour escaping from the leaf (transpiration) when the plant is not photosynthesising.
• Guard cells open and close due to the movement of water into and out of the cells by osmosis.

Question 10

2.3.2 Plant organ system

Root hair cell adaptation

Answer 10

• large surface area to volume ratio - increases their uptake of water by osmosis.
• cell membranes have lots of carrier proteins for the active transport of mineral ions.

Question 11

2.3.2 Plant organ system

Xylem tissue adaptations

Answer 11

• **transport water and mineral ions **from the roots to the stem and leaves.
• composed of hollow tubes strengthened by lignin.
• only moves upwards (due to the minerals and water only being needed in one location - leaves)
• Water moves through the plant due to transpiration.

Question 12

2.3.2 Plant organ system

Phloem tissue adaptations

Answer 12

• transport dissolved sugars from the leaves to the rest of the plant for immediate use or storage.
• composed of elongated cells which contain pores in their end walls to allow cell sap to move from one phloem cell to the next.
• moves up and down (bidirectional as it needs to move throughout the plant)
• The movement of sugars around the plant is known as translocation.

Question 13

2.3.2 Plant organ system

Transpiration

Answer 13

• xylem cell
• Water near the surface of the leaf evaporates, becoming water vapour and exiting the leaf through the stomata.
• water is drawn up from the xylem to replace the water lost from the leaves.
• This is known as a ‘transpiration stream’ or ‘transpiration pull’.

Question 14

2.3.2 Plant organ system

Factors affecting the rate of transpiration

Answer 14

Humidity:
* air is full of water vapour - reduces the concentration gradient of water vapour between the inside and the outside of the leaf.
* This reduces the rate as water vapour diffuses out of stomata more slowly.

Wind speed:
* the faster the wind speed, the faster the rate of transpiration
* windy conditions will move any water molecules hanging around outside of the leaf.
* This increases the concentration gradient = increases the rate of transpiration.

Temperature:
* higher temperature increases the rate of transpiration
* the water molecules have more kinetic energy so move faster out of the stomata.
* Higher temperatures also increase evaporation of water from a liquid to gaseous state.

Light intensity:
higher light intensity causes the stomata to be open for longer time periods
therefore the amount of transpiration will increase (gaseous exchange, water vapour diffuses out)