Plant Cells, Translocation And Transpiration

Question 1

Organs in a plant

Answer 1

• stems
• roots
• leaves
Work together as an organ system
Plant organs are made of tissues

Question 2

Tissues in a plant

Answer 2

• epidermal tissue - covers whole plant
• palisade mesophyll tissue - part of leaf where most photosynthesis happens
• spongy mesophyll tissue - contains big air spaces to allow gases to diffuse in and out of cells
• xylem and phloem - transport water, minerals ions and food
• meristem tissue - found at the growing tips of shoots and roots

Question 3

Functions of plant cell components

Answer 3

• epidermal tissues are covered with a waxy cuticle - helps reduce water loss by evaporation
• upper epidermis is transparent so that light can pass through to the palisade layer
• palisade layer has lots of chloroplasts for photosynthesis
• xylem and phloem - form network of vascular bundles which deliver water and other nutrients to entire lead - take away glucose produced by photosynthesis (also help support structure)
• tissues adapted for efficient gas exchange
• lower epidermis full of little holes (stomata) which let CO2 diffuse directly into the leaf
• opening/closing controlled by guard cells - response to weather conditions
• air spaces in spongy mesophyll tissue increase rate of diffusion of gases

Question 4

Phloem tubes transport food

Answer 4

• made of columns of elongated living cells with small pores in the end walls to allow cell sap to flow through
• transport food substances (dissolved sugars) to the plant for immediate use (growing regions) or storage
• goes in both directions
• translocation

Question 5

Xylem tubes take water up

Answer 5

• made of dead cells joined end to end and a whole down the middle
• strengthened by lignin
• carry water and mineral ions from roots to stems and leaves
• movement of water from the roots, through xylem and out of the leaves is called transpiration stream

Question 6

Transpiration

Answer 6

• loss of water from the plant
• caused by evaporation and diffusion of water from a plants surface
• mostly happens in the leaves
• evaporation creates a slight shortage of water in the leaf, more water is drawn up from the rest of the plant through xylem vessels to replace
• more water is drawn up from roots, so there’s a constant transpiration stream of water through the plant

Question 7

Factors affected by transpiration rate

Answer 7

• Light intensity - brighter the light, greater the transpiration rate
(because when stomata close, very little water can escape)
• temperature - warmer, faster transpiration happens because particles have more energy to evaporate
• air flow - better air flow, greater transpiration rate
• humidity - drier air around leaf, faster transpiration happens

Question 8

How can you estimate the rate of transpiration?

Answer 8

• measuring water uptake of the plant
• keep constant conditions

Question 9

Guard cells adaptations

Answer 9

• kidney shape which opens and closes stomata
• lots of water - guard cells go turgid which makes stomata open and close
• when plant is short of water, guard cells lose water and become flaccid making stomata close - stops water vapour from escaping
• thin outer walls and thickened inner walls to make opening and closing work
• sensitive to light and close at night - save water without losing out on photosynthesis
• more stomata on the undersides
• lower surface, shaded and cooler so less water is lost
Adapted to gas exchange and controlling water loss