Download cell sap

First Five
• Silently in your notebook answer the following:
• The drawing shows the outline of a human cell. Copy the drawing
and make two further drawings to show how the cell would appear
if it were to be immersed for a few minutes in a solution with:
• a lower water potential than its own cytoplasm
• a higher water potential than its own cytoplasm
• Cereal plants were growing in a field. The field was then flooded
with sea water. Suggest why the sea water causes plants to die.
Announcements
• Quiz: Thursday (M) and Friday (G) on Cell Structure,
Specialized Cells, Magnification, Diffusion and Osmosis
• Unit Exam: 28th and 29th
• Notebook Turn in: 28th and 29th
• Late work turn in: 25th
Additional Notes
• The cell sap and cytoplasm function as
fairly concentrated solutions.
• A plant cell in this condition is said to be turgid
• If all the cells in the plant are turgid, the plant
will be firm and upright and the leaves would be
expanded
Plant cells
cell wall
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vacuole
The cell absorbs water
by osmosis ....
cytoplasm and
cell membrane
....but the cell wall stops the
cell expanding any more
Fresh water fish
14
Trout
In fresh water fish, the blood is more
concentrated than the surrounding water
As a result the fish takes in water by osmosis
Not so much through the skin, which is thick,
but through the gills which have a very thin
membrane
14
Perch
The fish gets rid of the excess water by means of its kidneys
kidneys expel
excess water ...
blood carries water
to kidneys
gills absorb water
by osmosis
heart
...in the form of
dilute urine
Sea water fish
15
Herring
Sea water is a more concentrated solution than the
fish’s blood. What will be the osmotic effect ?
A sea water fish will lose water by osmosis through
its gills.
The fish drinks sea water and the gills expel the
excess salt from the blood, so keeping its
concentration constant
Question
What did you notice about the colour of the cell
sap in the two cells?
Can you suggest an explanation for this?
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Osmosis between cells
20
If the concentration of the cell sap is greater in one cell than
in its neighbour, water will pass by osmosis from the less
concentrated to the more concentrated.
cell sap more
concentrated
cell sap less
concentrated
Limp and turgid tissue
These cells are short of
water; the tissue is limp and
the plant is wilting
21
The cells have taken up
water by osmosis; the
cells are turgid and the
tissue is firm
23
In the growing regions of a plant, the cell walls are
not inextensible but are still ‘plastic’
When the vacuole takes in water by osmosis it
expands, pushing out on the ‘plastic’ cell wall
and increasing the size of the cell.
Cell division at a growing point increases the
number of cells but cell expansion causes the
increase in size.
Cell division followed by cell expansion causes
growth
24
Cell extension
1
2
3
1 The cell has just divided
2 Vacuoles start to form in one cell
3 The vacuoles absorb water by osmosis and start to extend
the cell
4 The vacuoles begin to join up and continue to absorb water
and extend the cell
4
Growth in a shoot tip
these cells will divide
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cell division
continues
vacuoles
forming
cells absorb water
by osmosis and
expand
Question 1
In osmosis, water will diffuse through a membrane
(a) From water to a concentrated solution
(b) From a concentrated solution to a dilute
solution
(c) From a dilute solution to a concentrated
solution
(d) From a dilute solution to a more
dilute solution
26
27
Question 2
Which statements are correct ?
(a) The plant cell wall is permeable to water
(b) The plant cell wall is selectively permeable
(c) The cell membrane is selectively permeable
(d) The vacuole contains a solution of salts and
sugars
Question
3
Cell sap
28
concentrated solution
a
c
dilute solution
b
more dilute solution
Water will tend to move by osmosis
(a) from b to a and c, and from c to a
(b) from c to a and b, and from a to b
(c) From a to b and c, and from c to b
(d) From c to b and a, and from b to c
Plant cells
Question 4
Which statements are correct ?
(a) A fresh water fish tends to absorb water
by osmosis
(b) A sea water fish tends to absorb water
by osmosis
(c) A fresh water fish tends to lose water to
its surroundings
(d) A sea water fish tends to lose water to
its surroundings
29
30
Answer
The colour intensity in the vacuole of the
left hand cell is greater than that in the right
This is because the uptake of water by
osmosis has diluted the cell sap in the
right hand cell
31
Correct
32
Incorrect