Transpiration & Translocation Lesson | GCSE Biology CIE Extended Triple

Transpiration & Translocation

This lesson covers:

How sugars are transported around the plant ('translocation')
How water and mineral ions are transported from the roots to the leaves
The factors that affect the rate of transpiration

Sources and sinks

1Sources - parts of the plant that create or release sucrose and amino acids.

2Sinks - parts of the plant that use or store sucrose and amino acids.

The concentration of sucrose and amino acids is higher at sources than at sinks.

Translocation

Translocation is the movement of sucrose and amino acids through the phloem, from sources to sinks.

Different parts of a plant act as sources and sinks at different times:

As a plant grows and develops, the direction of translocation changes.

In reality, this means that a single part of a plant may act as both a source and a sink at different times of the year.

Diagram showing sources and sinks in a plant with sources at the roots and sinks at the leaves.

1When leaves sprout in the spring:

Storage organs (e.g., roots) function as sources.
Growing leaves act as sinks, using nutrients for their rapid growth and development.

Diagram showing a plant with labelled sources and sinks. Sources are parts of the plant that create or release sucrose and amino acids, while sinks are parts that use or store them.

2When plants are growing in the summer:

Mature leaves act as sources, as they photosynthesise to produce sucrose.
Growing stems and reproductive structures (flowers and fruits) act as sinks, using the sucrose for energy.
Storage sites (roots, tubers, bulbs) also act as sinks, storing sucrose as starch.

Diagram showing a plant with the source labeled, indicating where sucrose and amino acids are created or released.

3When plants shed their leaves in the winter:

Storage sites (e.g. roots) become sources, releasing stored sucrose to sustain respiration in the rest of the plant.

Diagram showing the molecular structure of glucose.

Which part of the plant is glucose produced in?

Stem

Roots

Leaves

What do we call the movement of cell sap (a mixture of sugar and water) up and down the plant?

Translocation

Phloem cells have _________ in their end walls to allow cell sap to pass along the phloem tube.

stomata

starch

pores

lignin

What does the xylem transport in a plant?

Water and dissolved mineral ions

Water and dissolved sugars

Water only

Illustration showing a plant root hair cell absorbing water from the soil.

How do root hair cells absorb water from the soil?

Osmosis

Active transport

Diffusion

How do root hair cells absorb mineral ions from the soil?

Mass transport

Diffusion

Active transport

Osmosis

Which substance are xylem cells reinforced with to make them stronger?

Lignin

What is transpiration?

The release of energy in plant cells

The movement of water into the root hair cells

The evaporation of water from the leaves

What happens to the transpiration rate as the temperature increases?

It decreases

It increases

It stays the same

Are stomata normally open or closed during the night?

Open

Closed

Why does the rate of transpiration increase if the light intensity is increased?

The stomata open wider to let more carbon dioxide into the leaf for photosynthesis.

The root hair cells become more permeable to water, letting more water into the plant.

The humidity increases, which makes the rate of transpiration increase.

Illustration showing the effect of increased wind speed on a cloud.

What happens to the rate of transpiration if wind speed increases?

It decreases

It increases

It stays the same

Why does water loss slow down if a plant is put into a plastic bag?

The humidity increases

The temperature increases

The light intensity increases

During the summer, where does the primary production of sugars through photosynthesis occur in a plant?

Leaves

Flowers

Stems

Roots

Which of the following best describes the role of roots in a plant during the winter season?

Sources, actively photosynthesising

Sinks, using nutrients for growth

Sinks, storing excess sugars

Sources, releasing stored nutrients