Topic 2 - Organisation - Organising Plants

Question 1

Where is the epidermal tissue?

Answer 1

It covers the whole plant

Question 2

Structure of epidermal tissue?

Answer 2

1. The epidermal tissues aer covered with a waxy cuticle, which helps to reduce water loss by evaporation
2. The upper epidermis is transparent so that light can pass through it to the palisade layer
3. The lower epidermis is full of stomata, which let CO2 diffuse directly into the leaf

Question 3

What controls the opening and closing of the stomata?

Answer 3

Guard cells

Question 4

What is the palisade mesophyll tissue?

Answer 4

This is the part of the leaf where most photosynthesis happens

Question 5

Structure of the palisade mesophyll?

Answer 5

1. The palisade layer has lots chloroplasts
2. This means they are near the top of the leaf where they can get the most light

Question 6

What is the spongy mesopyll tissue?

Answer 6

1. It is a layer in the leaf that contains big air spaces to allow gases to diffuse in and out of cells
2. The air spaces help to increase the rate of diffusion of gases
3. They have a large surface area to make the diffusion of gases easier

Question 7

What is the meristematic tissue?

Answer 7

This is found at the growing tips of shoots and roots and is able to differentiate into lots of different types of plant cell, allowing the plant to grow

Question 8

What do the xylem and phloem do?

Answer 8

1. They form a network of vascular bundles which deliver water and other nutrients to the entire leaf, and take away the glucose produced by photosynthesis
2. They also help support the structure

Question 9

Describe the phloem?

Answer 9

1. Phloem tubes transport food
2. They are made of columns of elongated living cells with small pores in the end walls to allow cell sap to flow through
3. They transport food substances (mainly dissolved sugars) made in the leaves to the rest of the plant for immediate use or for storage
4. The transport goes in both directions
5. This process is called translocation

Question 10

Describe the xylem?

Answer 10

1. Xylem tubes take water up
2. Xylem is made of dead cells joined end to end with no end walls between them and a hole down the middle
3. They are strengthened with a material called lignin
4. They carry water and mineral ions from the roots to the stem and leaves
5. The movement of water from the roots, through the xylem and out of the leaves is called the transpiration stream

Question 11

What is the transpiration stream?

Answer 11

1. Transpiration is caused by the evaporation and diffusion of water from a plant’s surface. Most transpiration happens at the leaves
2. This evaporation creates a sligt 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
3. This in turn means more water is drawn up form the roots, and so there is a constant transpiration stream of water through the plants

Question 12

What four factors affect the transpiration rate?

Answer 12

1. Light intensity
2. Temperature
3. Humidity
4. Air flow

Question 13

How does light intensity affect transnpiration rate?

Answer 13

1. The brighter the light the greater the transpiration rate
2. Stomata begins to close as it gets darker. Photosynthesis cant happen in the dark, so they dont need to be open to let CO2 in
3. When stomata are closed, very little water can escape

Question 14

How does temperature affect transnpiration rate?

Answer 14

1. The warmer it is, the faster the transpiration rate
2. The water particles have more energy to evaporate and diffuse out of the stomata

Question 15

How does air flow affect transnpiration rate?

Answer 15

1. The better the air flow around a leaf, the greater the transpiration rate
2. If air flow around a leaf is poor, the water vapour just surrounds the leaf and doesnt move away. This means there is a high conentration of water particles outside the leaf well as inside it, so diffusion doesnt happen as quickly
3. If there is good air flow, the water vapor is swept away, maintaining a low concentration of water in the air outside the leaf. Diffusion then happens quickly

Question 15

How does humidity affect transnpiration rate?

Answer 15

1. The drier the air around a leaf, the faster transpiration happens
2. If the air is humid, there is a lot of water in it already, so there isnt much of a difference between the inside and the outside of the leaf
3. Diffusion happens fastest if theres a really high concentration in one place, and a really low concentration in the other