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

Ciliated Epithelium

• This tissue is found

lining the ends of

the bronchioles in

the lungs.

Squamous Epithelium

Plan Diagrams –

dicotyledonous leaf

Plan Diagrams -

dicotyledonous leaf

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

Animal Cell

Plant cell

Animal cell - answers

Plant

cell -

answers

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.

Diffusion across a membrane

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

Absorption and

Secretion of Materials

Unit 1

Cell Biology

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?

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