Download Sc 8 Unit 2 Topic 4 Notes

Science Focus 8
Cells and Systems
Topic 4
Topic 4 – Fluid Movement in Cells
* How do cells carry out everyday activities? Turn to page 128 of your textbook and read “Cell
Membrane”.
The Cell Membrane
A cell membrane that allows some substances to enter or leave the cell, while stopping other
substances
is
known
as
a
____________________
____________________
____________________ (SEMIPERMEABLE MEMBRANE). A PERMEABLE membrane
allows all materials through, while an IMPERMEABLE membrane does not allow anything
through.
semipermeable
membrane
Diffusion
The structure of the cell membrane controls what moves in or out of the cell. Particles - moving
in all directions, bumping into each other, eventually spread out evenly throughout the cell. We
know this process as DIFFUSION.
* Read more about diffusion on page 129. Make sure you take a look at Figure 2.12.
Diffusion plays a part in moving substances in and out of a cell. ____________________
determines the direction that a substance moves through the cell membrane. Particles move from
areas of high concentration to areas of low concentration. If there is an equal concentration
inside and outside the cell, the particles move in and out equally, but if the concentration of
particles on the inside is higher, the particles will move to the outside of the cell until an
equilibrium is reached. This is demonstrated by Figure 2.13A and Figure 2.13B on page 130 of
your textbook.
Science Focus 8
Cells and Systems
Topic 4
Osmosis
The diffusion of water through a selectively permeable membrane is called
____________________. Water helps to dissolve many of the substances involved in cell
processes. When water is lost (moves out of the cell) it leaves behind a high concentration of the
dissolved substances – when water moves back into the cell, the substances become more diluted
and can be used by the cell for its life functions.
* Turn to page 130 and 131 of your textbook and read “Osmosis”.
QUESTION 1:
The figure below is an example of osmosis. The water in the figure is moving from an area of
____________________ ____________________to an area of ____________________
____________________.
* Turn to page 134 of your textbook and read “Fluid Movement in Plants”. Also read the “Did
You Know?”.
Fluid Movement in Plants
Plants require a large supply of water to make sugars in the process of PHOTOSYNTHESIS. A
group of cells, that perform similar functions, are called ____________________. The
transportation of nutrients is the role of plant tissues.
QUESTION 2:
What are the two types of tissues inside plants called? Name the two tissues.
In a plant, the ____________________ TISSUES connect the roots to the leaves. The
____________________ TISSUE transports sugars manufactured in the leaves to the rest of the
plant, while the ____________________ TISSUE conducts water and minerals, absorbed by the
root cells, to every cell in the plant.
Science Focus 8
Cells and Systems
Topic 4
* Now turn to page 134 and 135 and read “From Root to Leaf”. Take a close look at Figure
2.17.
From Root to Leaf
The root system contains fine ROOT HAIRS. These hairs are extensions of epidermal cells.
When the concentration of water is greater on the outside of these root hairs, then water can pass
through the membrane by osmosis. This continues from cell to cell, until it reaches the xylem
tissue. The tube-shaped xylem cells then move the water by a build up of water pressure in the
root hairs (high pressure to low pressure) forcing the water up the xylem tissue, like water up a
straw, into the stems and leaves. Leaves are the plant’s food-producing organs (this is where
photosynthesis takes place). Photosynthesis takes place in the layer of cells that contain
chloroplasts (these cells are called palisade cells). They are thin, allowing a large amount of
light in (large surface area), and enabling the gases (in the air) to diffuse into the leaf cells. This
is displayed in Figure 2.19 of your textbook.
The tiny openings, called stomata, allow air to enter the leaf (supplying oxygen for respiration
and carbon dioxide for photosynthesis). The spaces between leaf cells allow the air to flow and
the guard cells open and close the stomata.
* Turn to page 135 of your textbook and read “Transpiration” and then turn to page 137 and read
“Pulling and Pushing”.
Transpiration
The loss of water (in a plant) happens through evaporation and is called
____________________. It is not a problem, unless, the plant loses too much water and doesn’t
replace it by the roots. The movement of water throughout the plant happens because of the
differences in pressure (high pressure in the root hairs to lower pressure in the leaves). This is
like pushing and pulling water throughout the whole plant.
QUESTION 3:
Turn to page 137 of your textbook and complete Topic 4 Review ____________________.