MakingFood

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DEFINITION

Osmosis is the net diffusion of water across a partially permeable membrane, from a solution with a high water concentration (HWC) to one with a low water concentration (LWC).

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Osmosis

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Osmosis

When water moves into a plant cell by osmosis it increases the pressure inside the cell.

The cell walls are sufficiently strong to withstand the pressure.

It is this pressure which keeps the cells rigid (maintains their turgor) and provides support.

Transpiration is the evaporation of water from the leaves of a plant.

The transpiration stream is the movement of water up the xylem (roots-stem-leaves).

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Why? So it is not blown / knocked over

How? The roots spread out over a large area to counterbalance the structures above the soil.

This also helps plants find water.

Functions 1. Anchoring the plant

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2. Absorb essential nutrients

Why? To take up substances to survive.

How? Roots have tiny hairs on their surface which increases their surface area to maximise absorption.

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3. Absorb water

Why? Water is a raw material for photosynthesis.

How? Root hairs increase surface area.

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Transport in Flowering Plants

In flowering plants there are separate transport systems for water and nutrients.

Substances are transported in vascular bundles made up of the xylem and the phloem.

Xylem Tissue

Transports water and minerals upwards from the roots to the stem and leaves.

The Xylem is made of dead cells joined into hollow tubes. They have thick strong walls made of lignin which give the plant support.

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Phloem tissue

Phloem tissue

Carries nutrients,

e.g. sugars made by photosynthesis, all round the plant.

The sugars are transported all round the plant especially to growing regions and the storage organs.

Phloem cells are alive and are made of 2 types of cells; sieve tubes and companion cells.

Sieve cell end walls have holes (pores) in them. Companion cells contain the cell nuclei.

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Sugar cane

Vascular bundles are composed of Xylem, Phloem and Fibres which support and protect the xylem and phloem.

Leaf Veins are Vascular Bundles.