Transport in Plants

Transport in Plants

Grade 8^th

​Plant Transport System

​8.1 Plant Transport System

• ​The roots, stem and leaves form a plant organ system for the transport of substances around the plant

• ​​Plants also possess two specialist transport vessels called the xylem and phloem

• ​The xylem and phloem are arranged throughout the root, stem and leaves in groups called vascular bundles​​

​Structure and function of the xylem

• ​Xylem vessels transport water and minerals from the roots to the stem and leaves

• ​The xylem has some key structural features

  • ​A substance called lignin is deposited in the cell walls which causes the xylem cells to die

  • ​Lignin strengthens the plant to help it withstand the pressure of the water movement

  • ​These cells then become hollow (as they lose all their organelles and cytoplasm) and join end-to-end to form a continuous tube for water and mineral ions to travel through from the roots

​Structure and function of the phloem

• ​Phloem vessels transport food materials (mainly sucrose and amino acids) made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem.

• ​The phloem has structural features different to the xylem

  • ​The cells are living cells and are not hollow

    ​The cells are joined end to end and contain pores in the end cell walls (called sieve plates) which allow easy flow of substances from one cell to the next

​Xylem?

​

Phloem?

​Vascular tissue in a dicotyledonous plant

Multiple Choice

The plant tissue that carries food materials DOWNWARD from the leaves to the rest of the plant is the ______.

• Phloem

• Stomata

• Chlorophyll

• Xylem

Multiple Choice

Vascular tissue that transports water and minerals UPWARDS from a plant's roots is know as ______.

• Chlorophyll

• Phloem

• Stomata

• Xylem

Multiple Choice

Which of the following is paired correctly:

• xylem : vessels

  phloem : sieve tubes

• xylem : sieve tubes

  phloem : vessels

​

​

​Which one dicot stem cross section

​A

​B

​8.2 Water uptake

• ​​Root hair cells are adapted for the efficient uptake of water (by osmosis) and mineral ions (by active transport)

• ​Root hairs are single-celled extensions of epidermis cells in the root

• ​They grow between soil particles and absorb water and minerals from the soil

• ​Root hairs increase the surface area to volume ratio significantly

  • ​This increases the rate of the absorption of mineral ions by active transport

• ​The high proportion of dissolved minerals and sugars in the cytoplasm (of the root hair cell) give it a low water potential (less watery)

  • ​​Water moves into the root hair cell by osmosis

The route of water through the plant

​Water moves, by osmosis, into the root hair cells, through the root cortex and into the xylem vessels:

• Once the water gets into the xylem, it is carried up to the leaves where it enters mesophyll cells

• So the pathway is:

root hair cell → root cortex cells → xylem → leaf mesophyll cells

Multiple Choice

How do water enter the roots from the soil?

• diffusion

• osmosis

• transpiration

• active transport

Multiple Choice

This is the definition for which word: The movement of particles down a concentration gradient (from a high concentration to a low concentration)

• Osmosis

• Diffusion

• Active transport

• Transpiration

​8.3 Transpiration

• ​​Transpiration is defined as the loss of water vapour from the parts of the plant that are above ground (leaves, stem, flowers)

• ​Loss of water occurs through evaporation of water at the surfaces of the spongy mesophyll cells followed by diffusion of water vapour through the stomata

• ​The many interconnecting air spaces between the mesophyll cells and the stomata creates a large surface area

• ​This means evaporation can happen rapidly when the stomata are open

Multiple Choice

Transpiration is

• the movement of water through a plant from the roots up the stem

• the loss of water from the leaves of a plant by the process of evaporation

• the flow of water into plant roots by osmosis from the soil

• the process of minerals and sugars moving through plant veins

​The effect of Transpiration

• ​​​Water moves through the xylem vessels in a continuous transpiration stream from the roots to the leaves via the stem to replace the water that has been lost due to transpiration

• ​Due to cohesion, the water in the xylem creates a continuous unbroken column (each individual molecule ‘pulls’ on the one below it)

  ​Transpiration produces tension or ‘pulls’ on the water in the xylem vessels

• ​If the rate of transpiration from the leaves increases, water molecules are pulled up the xylem vessels quicker

Multiple Choice

Why is the evaporation of water from leaves important?

• It cools leaves and helps move water up the plant.

• It makes the plant wilt

• It helps the plant to respire

​Movement water from root to leaf

​Structure of a plant is adapted to help it to take up water and move it up to plant

• ​The root hair cells provide a huge surface area which water can be absorbed

• ​The hollow, narrow xylem vessel provide an easy pathway for water to flow up

  ​Many air spaces inside leaf mean there is a large surface area of wet cells which water can evaporate

• ​The stomata when open allow water vapor diffuse easily out of leaf that creates low water potential

​Open and Close Stomata

​Review

There are several environmental conditions which have an impact on the rate of transpiration

​

• ​​Temperature

• ​Humidity

• ​Air movement

• ​​Light intensity

• ​Water supply​

Multiple Choice

What happens to the transpiration rate as light intensity increases?

• It increases

• It stays the same

• It decreases

Multiple Choice

What happens to the transpiration rate as humidity increases?

• It increases

• It stays the same

• It decreases

​Transpiration has several functions in plants:

• ​Transporting mineral ions

• ​Providing water to keep cells turgid in order to support the structure of the plant

  ​Providing water to leaf cells for photosynthesis

• ​Keeping the leaves cool, the conversion of water (liquid) into water vapour (gas) as it leaves the cells and enters the airspace requires heat energy. The use of heat to convert water into water vapour helps to cool the plant down

​Measuring transpiration rate

• ​A bubble potometer measures the uptake of water by a stem as a measure of the amount of water that is being lost by evaporation consequently pulling water up through the stem to replace

​Activity 8.2

​To see which part of a stem transport water and solutes

​Activity 8.4

​To measure the rate of transpiration of a potted plant

​Activity 8.3

​To see which surface of a leaf loses most water

​Uptake of ions in root

​

• ​Minerals cannot be absorbed by osmosis because this is the movement of water only. They cannot be absorbed by diffusion, because the minerals are in very low concentration. Instead, active transport is used.

• ​The root hair cells have carrier proteins in their cell membranes. These pick up the mineral ions and move them across the membrane into the cell against the concentration gradient.

​8.4 Translocation

• ​The soluble products of photosynthesis are sugars (mainly sucrose) and amino acids; collectively they are referred to as cell sap​

• ​​Phloem tissue transports dissolved sugars from the leaves to the rest of the plant for immediate use or storage

• ​​The transport of sucrose and amino acids in phloem, from regions of production to regions of storage or use, is called translocation

​8.4 Translocation

• ​Transport in the phloem goes in many different directions depending on the stage of development of the plant or the time of year; however, dissolved food is always transported from source (where it’s made) to sink (where it’s stored or used

​8.4 Translocation

• ​During winter, when many plants have no leaves, the phloem tubes may transport dissolved sucrose and amino acids from the storage organs to other parts of the plant so that respiration can continue

• ​During a growth period (eg. during the spring), the storage organs (eg roots) would be the source and the many growing areas of the plant would be the sinks

• ​After the plant has grown (usually during the summer), the leaves are photosynthesizing and producing large quantities of sugars; so they become the source and the roots become the sinks – storing sucrose as starch until it is needed again

Multiple Choice

Where does sugar transport begin?

• Roots

• Leaves

• Root hairs

• Vascular bundles

​8.4 Translocation

Multiple Choice

Plant transports food made in the leaves to __________. 

• roots 

• stem

• flowers 

• all of the above

Multiple Choice

What is the best words to describe sugar source and sugar sink

• Both are plants organ and act as storage

• Sugar sink can be either roots, fruit or mature leaves and sugar source is shoots

• Sugar source act as site for sugar production and sugar sink will store sugar

• Companion tube carry food from a sugar source to a sugar sink