Download SAPS - 2 Plant cells and water - student sheet

Plant Cells and Water
Students’ Sheet
Introduction
Cells are basic building blocks from which living
organisms are made. You can see them through a
microscope. Each plant cell has a cell wall, cell
membrane, cytoplasm, nucleus, vacuole,
mitochondria and chloroplasts. There are different
types of cells.
From atoms to cells
Atoms are the building blocks of all
matter. Any one cell is made from about
100 trillion atoms, that’s:
100 000 000 000 000 atoms!
Groups of similar plant cells form tissue and work
together to do a particular job, for example, root
hair tissue (enables water and dissolved minerals
to get into a plant) and xylem (tubes that carry
water around a plant).
99% of these are atoms of the elements
hydrogen, carbon and oxygen. About a
half are hydrogen atoms.
Groups of different tissues make up an organ,
again working together to do a particular job. A
leaf and a plant root are examples.
7 400 000 000 people
For comparison, the world’s population
is about
The next stage in ‘building’ a plant is for organs to
work together as an organ system to do a
necessary job, for example, a reproductive system
and a leaf canopy. All living organisms (plants
and animals) consist of a number of organ systems.
So if each person represented an atom
you would need about thirteen and a
half thousand times the number of
people living on Earth to make one cell!
To understand how water gets into and travels through plants you need to know something about
cells, tissues and organs in plants.
Activities
Activity 1: Plant cells
The root hairs are tissue consisting of specialised cells called root hair cells.
epidermal cell
root hair cell
Science & Plants for Schools: www.saps.org.uk
Plants Cells and Water: p. 1
Questions
1. Look at the diagram of a root hair cell and match these names to the letters: Cell membrane,
Cell wall, Cytoplasm, Nucleus, Vacuole.
A
B
C
D
E
2. Describe the difference between an epidermal cell and a root hair cell.
3. Two other components found in all plant cells are mitochondria and chloroplasts. Describe
where these are found in a root hair cell.
4. A plant’s root hair cell is about 0.015 mm in diameter and 1-2 mm in length. How many time
bigger is the diameter of a root hair cell than a carbon atom?
Size of atoms and cells
Diameter of atoms in nanometres (nm):
hydrogen = 0.11 nm; carbon = 0.34 nm; oxygen = 0.30 nm
[0.1 nm = 0.0000001 mm]
Activity 2: Investigating potato sticks
1. Pour about 200 cm 3 of water into each of two screw cap jars.
2. Add 2 teaspoons of salt to one of the jars and stir until the salt has dissolved.
3. Slice a potato into four sticks, each about 5 cm x 1 cm x 1 cm. Try bending them gently and
make a note of how flexible they are.
4. Place two sticks into each of the jars and leave overnight, preferably in a fridge or somewhere
cold.
5. Remove the potato sticks and describe any changes that happened overnight. Compare their
sizes, shapes and flexibility.
Observations
Make a table to compare the potato sticks
(a) before being placed in the jars
(b) after being immersed in water overnight
(c) after being immersed in salty water overnight.
Compare your observations with others in your class and suggest what you think happened.
Science & Plants for Schools: www.saps.org.uk
Plants Cells and Water: p. 2
Activity 3: Water and cell membranes
Cell membranes are partially permeable. This means that some very small particles can pass
through, but not larger ones. This includes water molecules. You can investigate this using
dialysis tubing (you may know it as Visking tubing).
Visking tubing is flat. Soaking it in water softens the tubing, which can then be opened up by
gently rubbing it between finger and thumb. ‘Cells’ can be made by tying one end to seal it,
pouring in a liquid and sealing the other end (see diagram below).
10 cm length
of flat Visking
tube soaked
in water
tube is
opened up
and one end
folded over
and tied
liquid poured
into tube and
other end
folded over
and tied
Modelling a cell membrane
Work in a group of four to prepare the following set ups:
B
A
C
D
In beaker:
water
water
sugar solution
sugar solution
In ‘cell’:
water
sugar solution
water
sugar solution
Sugar solution is 17 g / 100 cm 3 (0.5 mol dm-3)
Observations
Make a table similar to the one below to record your group’s observations.
Set-up
Observations
A
B
C
D
Science & Plants for Schools: www.saps.org.uk
Plants Cells and Water: p. 3
Questions
Here are ‘exploded’ diagrams to show the arrangements of particles in water and in a solution of
sugar in water.
Key
water particle
sugar particle
water
sugar in water
In reality the particles in both cases are closer together (almost touching). Scientists often use
exploded diagrams to make the particles easier to see. In water and in sugar solution, particles
move freely and randomly.
1. Using diagrams above try to describe any changes you observed in the four experiments: A, B,
C, D.
2. Explain the changes using the concept of particles and diffusion.
3. The type of diffusion you observed is called osmosis. In your own words explain what happens
during osmosis.
Science & Plants for Schools: www.saps.org.uk
Plants Cells and Water: p. 4