Learning Outcomes 1
• To revise the basic structure of plant
and animal cells
• to discuss the similarities and
differences between animal and plant
cells.
• Identify variation in structure between
cells within a tissue
Introduction to Cells
• Cell
– The basic unit of life
– Smallest structure able to lead independent life
and show all characteristics of living things.
– There are seven characteristics – Movement,
Reproduction, Sensitivity, Growth, Respiration,
Excretion and Nutrition (MRS GREN)
• Nucleus
– contains the genetic information, controls the
cell.
Learning Outcome 2
• To observe a variety of different tissues
• To recognize and account for the
variation in structure of the following
tissues
– Columnar, ciliated and glandular epithelia
– Palisade and spongy mesophyll
– Xylem and phloem
Cell Theory - Starter
• The cell is the fundamental unit of life. All organisms, whatever their type or size, are composed of cells. The modern theory of cellular organisation states:- – All living things are composed of cells and cell
products.
– New cells are formed only by the division of pre-existing cells
– The cell contains inherited information (genes), which is used as instructions for growth, functioning and development.
– The cell is the functioning unit of life; the metabolic reactions of life take place within the cells.
Cell Theory - Question
• Before the development of cell theory,
it was commonly believe that living
organisms could arise by spontaneous
generation.
• Explain what this term means and why
it has been discredited as a theory.
Multi-cellular organisms
– Cells tissues organs organ systems
organism
– Division of labour – a tissue is a group of cells
specialised to carry out a particular function.
Cell Variety
– Variation within one tissue e.g. blood
contains red blood cells and white blood
cells
– Variation between different tissues e.g.
compare xylem and phloem
Structure in Relation to Function
• The structure of each cell is exactly tailored
to suit its function.
• Advantage of specialisation
– Ability to function at a higher level
Tissues
• You should be able to discuss the structure and function of the tissue types, and discuss how their structure suits their function. – e.g. describe how a xylem vessel is structurally
suited to perform 2 functions.
• FOR THE ACTIVITY BELOW GIVE TISSUE, CELL TYPE, SPECIALISED STRUCTURAL FEATURES AND FUNCTION. – Choose 3 of the human tissues try to relate
structure to function.
– Choose 3 of the plant tissues try to relate structure to function.
Homework Questions (10 marks)
• By means of two examples, show how
the differences between the structure
of cells in different tissues are related to
the different functions of these tissues.
Learning Outcome 3
• To observe plant cells from fresh tissue,
using a stain.
• To observe prepared slides of plant
and animal cells and tissues.
Cell Biology and Microscopy
• When Scientists began to observe cells,
they started with simple microscopes.
Today two different types of
microscope are in use, both
microscopes use a form of radiation to
create an image of the specimen:
– Light microscope – uses light
– Electron microscope – uses electrons
Using a light microscope
Magnification
– Number of times larger an image is
compared with the real size of the object
Resolution
– The ability to distinguish between two
separate points
Structure of a generalised animal cell as seen with a
very high power quality light microscope
(diameter ~ 20ųm)
Structure of a generalised plant cell as seen with a
very high power quality light microscope
(diameter ~ 40ųm)
Light Microscope
• For the microscope in front of you,
work out
– The magnification of each lens
– The field of view for each lens
• Using a graticule / stage micrometer
• All diagrams should include title,
labels, magnification
Learning Outcome 4
• Identify an appropriate example of a
unicellular organism
• To know the functions of each of its
most obvious organelles
Unicellular Organisms (one
cell) • A unicellular organism must make all
chemicals and perform all functions
necessary for life.
– Pleurococcus is a unicellular plant
– Paramecium is a unicellular animal
– Euglena is a unicellular organism, which demonstrates characteristics of both plant
and animal cells.
Summary Questions
• Why is the cell described as the basic unit of life?
• Explain the meaning of the terms unicellular and multicellular organism.
• Describe the roles played by a named unicellular plant’s cell wall, nucleus and chloroplast.
• Describe the role played by a food vacuole and a contractile vacuole in a unicellular animal.
Extended Response Question
• Give an account of the differences
between uni-cellular and multi-cellular
organisms, including examples of
each.
– Marks available = 10
• Maximum of 8 marks for content
• Coherence 1 or 0
• Relevance 1 or 0
Learning Outcome 5
• To state the overall cellular function
associated with a particular cell
organelle
• To identify some organelles in an
electron micrograph
Questions
1. State three differences that exist between
a typical plant and a typical animal cell.
2. Name three organelles common to both
plant and animal cells.
3. State a structural difference between
rough and smooth endoplasmic reticulum.
4. Explain briefly why a liver cell may contain
as many as one thousand mitochondria.
5. Why do the cells in a frog tadpole’s tail
contain many lysosomes?
Learning Outcome 10
• To describe the structure of the plasma
membrane
• To describe the methods of absorption
and secretion.
• To investigate the chemical nature of
the Plasma membrane.
Absorption and Secretion
• Absorption
– The uptake of materials by a cell from its
external environment
• Secretion
– The discharge of useful intracellular
molecules into the surrounding medium
by a cell
Methods of A and S
• Diffusion
• Osmosis
• Active transport
• Endocytosis
– Phagocytosis
– Pinocytosis
• Exocytosis (secretion)
Cell boundaries
• All living cells are surrounded by a
plasma membrane.
• Plants cells are also surrounded by a
cell wall.
Structure of the Plasma
Membrane
• The plasma membrane is composed of
phospholipids and proteins.
• The current theory is a fluid mosaic
model
– Fluid layer of moving phospholipids
– Patchy mosaic of protein molecules
Investigating the chemical
nature of the cell membrane • The cell sap present in the central
vacuole of a beetroot cell contains red
pigment.
• “Bleeding” indicates that the cell’s
plasma and vacuolar membranes
have been damaged.
• You are going to investigate the
chemical nature of the plasma
membrane using beetroot cylinders.
The results
• In which test tubes did “bleeding”
occur and why?
• Think think think think think think think
– Structure of plasma membrane
– How would each of the conditions affect
it?
– Which test tube was the control?
Explanation
• “bleeding” occurs in B, C, and D, it can be
concluded that the cell membranes have
been destroyed in each of these tubes.
• Acid and high temperature destroy the
membrane by denaturing the protein
molecules.
• Alcohol dissolves the phospholipid (fat)
component of the membrane.
• These allow the red pigment to escape.
Learning Outcome 11
• To discuss cell membrane structure with
relation to the fluid mosaic model
• To explain the function of the plasma
membrane in relation to active
transport and the absorption and
release of materials.
• To handle data concerning the solute
concentration in aquatic organisms
Structure of the plasma
membrane • The plasma membrane is a fluid phospholipid
bilayer, with a mosaic of protein molecules.
Diffusion
• Diffusion
– The net movement of molecules or ions
from a region of high concentration to a
region of low concentration.
– Diffusion occurs along a concentration
gradient.
Factors affecting the rate of
diffusion
• Concentration gradient – Greater the difference in concentration the greater the
rate of diffusion
• Temperature – At higher temperature kinetic energy particles increases
– Diffusion is faster
• Surface area – Greater the surface area, more particles can cross
– Increases rate of diffusion
• Nature of molecules or ions – Large molecules diffuse slower
– Non-polar molecules diffuse more easily
Active transport
• Active transport is the uptake of
molecules or ions against a
concentration gradient using energy
from respiration’
• Helps to build up a high concentration
of molecules/ions inside the cell.
• Special carrier proteins in the
membrane actively transport specific
molecules and ions.
Active Transport
• Examples include:
– Muscle contraction
– Absorption of mineral ions by roots
– Excretion of urea by the kidney
Learning Outcomes
• To understand osmosis
• To understand the role of the cell wall
• To discuss the cell wall with reference to cellulose fibres and permeability.
• To understand bulk transport
Absorption and Secretion
Revision
• Absorption – Uptake of materials by a cell from it’s
external environment.
• Secretion – Discharge of molecules into the
surrounding medium by the cell
• This movement is normally by:- – Osmosis, diffusion or active transport.
Diffusion and Osmosis
Definitions
• Diffusion
– T he net movement of molecules or ions from a
region of high concentration to a region of low
concentration.
– Diffusion occurs along a concentration gradient.
• Osmosis
– The net movement of water from a region of high
water concentration (HWC) to a region of low
water concentration (LWC)through a selectively
permeable membrane.
Osmosis
• All cell membranes are permeable to water to a small degree, because water molecules are able to diffuse through the phospholipid bi-layer.
• Some membranes are as much as a thousand times more permeable due to the presence of aquaporins (transmembrane proteins acting as water channels)
Osmosis • Example:
– Two solutions are separated by a partially
permeable membrane. Solute molecules are too
large to pass through pores in the membrane, but
water molecules are small enough.
What would happen if the
membrane were not present?
• Net movement of solute molecules
from B to A by diffusion
• Net movement of water molecules
from A to B by diffusion
• Equilibrium – concentrations of water
molecules and solute molecules in A
would equal that in B.
What will happen if the membrane
is present?
• Solute molecules too large to pass through membrane
• Water molecules pass easily from A to B
• Net movement of water from A to B until equilibrium is reached, i.e. solution A has the same concentration of water molecules as solution B.
• The level of liquid A will fall and the level of liquid B will rise.
• Equilibrium is brought about by the movement of water molecules alone.
Osmosis in red blood cells
• If a red blood cell is placed in a
hypotonic solution it will burst
• If a red blood cell is placed in an
isotonic solution there is no net
movement of water and the cell
remains unchanged
• If a red blood cell is placed in a
hypertonic solution is will shrink
(crenate)
Normal red blood cell containing 0.85% dissolved solute
Surrounded by a solution containing 0.85% salt
Cell swells and bursts
Surrounded with pure water
Surrounded with a solution containing
1.7% dissolved solute No change
shrinks
Effect of osmosis on blood cells
Plant cells
• If a plant cell is placed in a hypotonic
solution it becomes turgid
• If a plant cell is placed in an isotonic
solution there is no net movement of
water and the cell remains unchanged
• If a plant cell is placed in a hypertonic
solution it becomes plasmolysed
Surrounded
by pure water
Surrounded by a
solution containing
10% sugar
Plant cell containing
3% dissolved solute
Surrounded by
solution containing
3% sugar
Turgi
d
Plasmolyse
d
Effect of osmosis on plant cells
Osmoregulation in
Paramecium • Paramecium lives in
fresh water
• it continuously gains
water by osmosis
• The cell is prevented
from bursting by the
presence of
contractile vacuoles
Contractile Vacuoles
• canals collect excess water
• when swollen the vacuole contracts
and discharges it contents through a
pore
• The two contractile vacuoles discharge
their contents alternately
Bulk Transport
• Endocytosis - Absorption
– Engulfing of molecules into the cell
– Phagocytosis – large molecules
– Pinocytosis – liquids
• Exocytosis – secretion
– The release of large molecules to the
outside of the cell
Cell Wall
• cell wall is composed of cellulose fibres.
• Consists of two layers.
– primary wall is random arrangement of
cellulose fibres.
– secondary wall consists of layers of closely
packed fibres of cellulose laid down like a
mesh
• spaces between the cellulose fibres
are filled with water
– Water moves easily from cell to cell