Download cell wall - take2theweb

Absorption and Secretion
•State the definition of diffusion.
Molecules move from a higher concentration to a lower
concentration down a concentration gradient
•Explain how diffusion could be used by a cell to absorb
molecules.
The substance must be at a higher concentration outside
the cell for it to diffuse into the cell
•Give two examples of molecules that would enter a cell by
diffusion.
Glucose
amino acids
oxygen
Explain how diffusion could be used by a cell to pass molecules
out. The molecules must have a higher concentration inside the
cell compared to outside
•Give two examples of molecules that would be passed out of a
cell by diffusion.
carbon dioxide
urea
•State the definition of osmosis.
Water molecules moving from a higher concentration to a
lower concentration passing through a selectively permeable
membrane
Explain what would happen if an animal cell was surrounded by
a solution with a higher water concentration.
Water molecules would move into the cell by osmosis from
high concentration outside cell and it would burst as it only has
a plasma membrane
•Explain what would happen if a plant cell was surrounded by a
solution with a higher water concentration.
Water molecules would move into the plant cell by osmosis
from high concentration outside cell and it would become
turgid as it has a cell wall to prevent it bursting
•In both cases above which solution can be called hypotonic?
The surrounding solution or the cytoplasm of the cell?
The solution surrounding the cell is hypotonic to the cell sap
Why do plant cells and animal cells react differently to this
higher water concentration outside the cell?
Plant cells have a cell wall made of the carbohydrate cellulose which
prevent the cell from bursting
Explain what would happen if an animal cell was surrounded by
a solution with a lower water concentration.
Water molecules would move out of the cell by osmosis from
high concentration inside cell and the animal cell would shrivel
up
•Explain what would happen if a plant cell was surrounded by a
solution with a lower water concentration.
Water molecules would move out of the cell by osmosis from
high concentration inside cell and the plant cell would become
plasmolysed and membrane moves away from the cell wall
•Explain the following terms
Hypertonic This is a liquid that has a lower water
concentration
Isotonic
This is liquids with equal water concentration
Hypotonic
This is a liquid with a higher water concentration
•List two components of a plasma membrane.
phospholipid bi layer and proteins
•List two different proteins found in a plasma membrane.
protein pores and carrier proteins
•Explain why the plasma membrane is based on the fluid mosaic
model.
Fluid because the phospholipid layers are moving
Mosaic because the proteins produce a pattern in the
phospholipid layers
Why is the plasma membrane described as selectively
permeable?
It only allows small soluble substances to pass through
•How could each component of the plasma membrane be
destroyed in an experiment?
When the cells are heated to above 50 oC the proteins in the
plasma membrane become denatured
If the cells are immersed in alcohol the phospholipid layer is
destroyed
•Label the diagrams below of a plasma membrane.
Label the phospholipid bi layer, carrier proteins and protein
pore
•Describe the structure of the cell wall.
Cell wall is made of cellulose fibres
Is the cell wall selectively permeable like the plasma
membrane?
The cell wall is full permeable
•Explain the term selective ion uptake (active transport).
This is when a cell takes in certain molecules(ions) against a
concentration gradient using energy from aerobic respiration
•Give an example of an ion that would be taken into a cell by
this method.
sodium
potassium
•Why is it called selective?
It will take in more of one ion than another
What are the main differences between selective ion uptake
compared to diffusion and osmosis?
Diffusion and osmosis do not use energy as the molecules move
down a concentration gradient
Label the phagocyte blood cell engulfing a bacteria using
phagocytosis.
•Make sure you have labelled the following in the diagram
above:
Lysosomes
Food vacuole
• What is the role of the lysosomes in phagocytosis?
They contain digestive enzymes to breakdown the engulfed
bacteria
Explain pinocytosis.
A method of certain cells taking in liquids
NB You should be able to discuss the following:
Experiment to measure the water concentration of cell sap
using plant tissue.
Experiment to investigate the chemical nature of the plasma
membrane
Interpret data concerning solute concentration in aquatic
organisms in their environment.
List the 5 main techniques that cells use to absorb or secrete
substances.
Diffusion
Osmosis (water)
Active transport (selective ion uptake) needs energy
Phagocytosis using the organelle called lysosomes
Pinocytosis