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Movement of Substances

Active Transport in Root Hair Cells.

The tips of the roots that are deep in the soil, have root hairs. These

are very thin hair-like cells that emerge from the root tip.

Root hair cells have to be able to absorb large amounts of water, as the

transpiration stream pulls up water to the leaves. As the process relies on

diffusion, the cells must present a large surface area to the surrounding

soil the rate of diffusion is directly proportional to the surface area -

!icks "aw#. Thus, the cell wall facing the soil is elongated outwards.

Mrs. $. %be&er 'rech (.%d.)ons.#

The root hairs are in the soil. *nside the root hairs

there is a lot of water because the cytoplasm and

vacuole are rich in water. They also have lots of

minerals and nutrients.

+hen it rains, or when we water the plants, there is

more water in the soil than in the cell, so water enters

by osmosis.

+hen we give nutrients to the soil, by adding

fertilisers, manure etc., the minerals enter the root

hairs by passive diffusion.

(ut sometimes, in the soil, there may be less nutrients,

and sometimes, less water too. (ut the plant still needs

to absorb water and minerals, because the root hairs

need to take these up from the soil and supply all the

other cells in the plant. So in this case, nutrients andminerals enter the root hair by   _____________ and not by diffusion, because the process

occurs against a concentration gradient.

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Movement of Substances

Past paper question from Annual Form 3 JL Exam 2!.

The following diagram shows part of a root in soil.

a. "abel the diagram with these words cell "all# vacuole# c$toplasm#

nucleus# soil particle# root %air

b. ame the process by which water is absorbed by the roots from the

soil. / mark#

c. Mineral salts in the form of ions are drawn into the roots along with

the water. They are taken up partly by passive diffusion. )owever they

can be absorbed by the roots even when they are present in the soil in alower concentration than inside the root cells. ame the process by

+hich mineral salts can be taken up into the root cells when they are

present in a low concentration in the soil0 / mark#

Total& ' mar(s

Mrs. $. %be&er 'rech (.%d.)ons.#

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Movement of Substances

1smosis is very important in root hair cells. 2roviding that the soil is

moist, it is possible for water to enter the root hair by osmosis. +ater

passes from a region of high water concentration wet soil# through asemi-permeable membrane the cell membrane# to a region of lower water

concentration the cytoplasm#. This makes the cell turgid. As these cells

develop they absorb water by osmosis and the hair can be pushed

between soil particles. The role of the root hairs is that they increase

the surface area between the root and the soil this is necessary for the

absorption of water and mineral salts.

Mrs. $. %be&er 'rech (.%d.)ons.#