Chapter 2

CellsCellsThe Building

Blocks of Life

• Cells observed under the light microscope.

Animal CellPlant Cell

Recollection ActivityRecollection Activity

• Drawing of cells observed under the light microscope.

Animal CellPlant Cell

Recollection ActivityRecollection Activity

• Drawing of cells observed under the light microscope.

Animal CellPlant Cell

Recollection ActivityRecollection Activity

• Are the basic structural and functional units of life

• Cells can exist:– Singly as independent unicellular

organisms – As part of multicellular organisms

• Such cells are modified for specific functions

What are Cells?

Amoeba Feeding

What characteristics would a cell need to carry out its functions?

What characteristics would a cell need to carry out its functions?

•Area for respiration•Area for reactions•Control Centre•Storage of genetic material

•Barrier to control movement of materials

Cell Structure:

PROTOPLASM – The Living Matter of Cells

Cell Structure:

PROTOPLASM – The Living Matter of Cells

PropertiesProperties•Mixture•70-90% water

•Mineral salts and organic compounds

(2) Cytoplasm(2) Cytoplasm

(3) Plasma/Cell(3) Plasma/Cellmembranemembrane

(1) Nucleus(1) Nucleus

Consists of:Consists of:

Cell Structure:

(1) Nucleus – The Control Centre

Cell Structure:

(1) Nucleus – The Control Centre

StructureStructure• Nuclear membrane/envelope• Nucleolus• Chromatin• Nucleoplasm

FunctionFunction

• Control centre for cell’s activities• Control cell division• Contains genetic materials

Chromatin condenses during cell

division

chromatin

chromosome

histones

Cell Structure:

(2) Cytoplasm – The laboratory

Cell Structure:

(2) Cytoplasm – The laboratory

PropertiesProperties• Colloidal (glue-like);• Mainly water with salts & sugars• Larger molecules of fats &

proteins • Endless chemical reactions

taking place• With many small structures

called organelles

Cell Structure:

(2) Cytoplasm – The Control Centre

Cell Structure:

(2) Cytoplasm – The Control Centre

Organelles in the cytoplasmOrganelles in the cytoplasm

Present in Plant & Animal Cellsa)Ribosomesb)Rough Endoplasmic Reticulum (RER)c)Smooth Endoplasmic Reticulum (SER)d)Golgi Apparatus/Bodye)Mitochondriaf)Vacuole(s)

Present in Plant Cells onlya) Chloroplasts

Cell Structure:

(2a) RibosomesCell Structure:

(2a) RibosomesStructureStructure

Small Round StructuresEither attached to ER or lie freely in cytoplasm

FunctionFunction

Protein synthesisRibosomes on RER: Proteins are transported out of the cellFree Ribosomes: Proteins used within the cytoplasm of the cell

Cell Structure:

(2b) Rough Endoplasmic Reticulum (RER)Cell Structure:

(2b) Rough Endoplasmic Reticulum (RER)

StructureStructure

Membrane network continuous with the nuclear envelope.Ribosomes attached to its outer surface.

FunctionFunction

Transports proteins made by ribosomes to the golgi apparatus for secretion out of the cell.

2D diagram to show RER

Cell Structure:

(2c) Smooth Endoplasmic Reticulum (SER)Cell Structure:

(2c) Smooth Endoplasmic Reticulum (SER)

StructureStructure

Membrane network connected to the RERAbsence of Ribosomes

FunctionFunction

Synthesizes substances such as fats and steroids (e.g sex hormones)Detoxification

2D diagram to show SER

Cell Structure:

(2d) Golgi apparatus/bodyCell Structure:

(2d) Golgi apparatus/body

StructureStructure

Stack of flattened spaces surrounded by membranes

FunctionFunction

Stores and modifies substances made by the ERPackages these substances in vesicles for secretion out of the cell

2D diagram to show Golgi body

Synthesis and Transport of substances out of the cell

cristae

Cell Structure:

(2e) MitochondriaCell Structure:

(2e) Mitochondria

StructureStructure

Sausage-shaped organellesHighly folded internal membrane (cristae)Double membrane

FunctionFunction

Carries out cellular respirationDuring respiration, Glucose is oxidised to release energyEnergy stored in small molecules called ATP

Cell Structure:

(2f) Vacuole(s)Cell Structure:

(2f) Vacuole(s)

StructureStructure

Fluid filled space enclosed by a membrane

FunctionFunctionAnimal Cell

•Many small vacuoles•Contains water and food substances• Usually exists temporarily

Plant Cell•One large central vacuole•Contains cell sap (Dissolved substances e.g sugars, mineral salts and amino acids)

Cell Structure:

(2g) CentriolesCell Structure:

(2g) Centrioles

FunctionFunction

Plays a part in cell division

Cell Structure:

(2h) ChloroplastsCell Structure:

(2h) Chloroplasts

StructureStructure

Disc-like structures found in leaf cellsContains a chlorophyll - green pigment

FunctionFunction

Carries out photosynthesisChlorophyll absorbs light energy which is converted to chemical energy

Cell Structure:

(2) Plasma/Cell MembraneCell Structure:

(2) Plasma/Cell Membrane

PropertiesProperties• Present in ALL living cells• Made up of fats and

proteins• Porous• Partially permeable• Controls the exchange the

substances between the cells and their environment

Cellulose Cell Wall

• Function–Provides shape to the plant cells–Protects cell from injury

• Adaptation–Cellulose is a hard structure–Fully permeable

Comparing plant and animal cellComparing plant and animal cellComparing plant and animal cellComparing plant and animal cell

Plant Cell Animal Cell

Cells Have Large Surface Area-to-Volume Ratio

Observing Cells

Microscopes are required to visualize cells.• Light microscopes

– can magnify objects up to 1000 x– Light micrographs are colour images

• Electron microscopes – can magnify objects up to 200 000 x– Electron micrographs are black-and-white

images

2.1 Cell structure and organisation

• Two ways of cutting a cell

Longitudinal (top-down) Transverse (sideways)

Endomembrane System

• Putting it all together

DNA directs RNA synthesis RNA exits nucleus through a nuclear

pore into RER ribosomes in RER synthesise protein proteins travel along RER proteins are modified in RER and

lipids are made in SER

Endomembrane System• Putting it all together

vesicles containing the proteins and lipids bud off from the ER

ER vesicles merge with Golgi body proteins and lipids enter Golgi body each is fully modified as it passes

through layers of Golgi body modified products are tagged, sorted

and bud off in Golgi vesicles

Endomembrane System

• Putting it all together Golgi vesicles either merge with

the plasma membrane and release their contents OR remain in the cell and serve a purpose

Transport Pathway by ER & GA

Differences between an animal cell and a plant cell

Animal cell Plant cell

Chloroplast absent Chloroplast present

Cellulose cell wall absent

Cellulose cell wall present

Contains vacuoles which are small and numerous

Contains one to a few large vacuoles filled with cell sap

The cytoplasm fills the cell

The cytoplasm is reduced to a thin lining

Centrioles present Centrioles absent

Division of Labour• In a multicellular organism, each type of cell specialises in performing one particular function.

E.g.

-The red blood cells in humans specialise in carrying oxygen around the body.

-The guard cells in a plant regulates gaseous exchange.• Thus the functions of a multicellular organism as a whole are divided among its different specialised cells (performing a particular function efficiently).

This dividing up of the functions is

called division of labour.

DifferentiationDifferentiation

DifferentiationDifferentiation

Red blood cell

Muscle cell Epithelial cell

Nerve cell

Xylem vessel cell

Root Hair cell

Process in which cell becomes

specialised and acquire special structures and

functions.

Process in which cell becomes

specialised and acquire special structures and

functions.

DifferentiationDifferentiation

From Cells to TissuesWithin a multicellular organism,

Cells of the same type are often arranged in groups to form a simple tissue.

Some simple animal tissues are designed to:

Move a bone/organ by contraction

Protect the structures beneath them

Muscle tissue Epithelial tissue

From Cells to TissuesWithin a multicellular organism,

Cells of different types can be arranged in groups to form a complex tissue.

The different cells work together to perform A SINGLE function.

Some complex animal tissues are designed to:

Carry electrical impulses

Join all parts of the organism

Nerve tissue Connective tissue

Some simple plant tissues are designed to: Protect a plant against injury and drying-out of its inner

parts

Epidermal tissue

Some complex plant tissues are designed to:

Vascular tissue

Carry out photosynthesis

Photosynthetic tissue

Transport food and water to various parts of a plant

From Cells to Tissues

From Tissues to Organs• Different tissues in organisms are often grouped

together to form an organ.It is responsible for carrying out more complex functions.

•Most animal organs (heart, lungs, skin) are made up of connecting tissues and some other specialised tissues.

The stomach wall consists of glandular, muscular and connective

tissues

The heart consist of muscular, blood and connective tissues

An organ performs a number of different functions.

E.g. Our liver stores food and produces bile.

• Most plants have organs such as leaves, stems, roots and flowers

epidermis

vascular tissues

vascular bundle

epidermis

• Every plant organ often performs many different functions.

For example, the stem of a plant has 3 main functions:

1. It transports water with dissolved mineral salts from the roots to the leaves.

2. It carries food from the leaves to other parts of the plant.

3. It provides support to the plant to stand upright.

From Organs to Systems•Different organs are then linked together to form a body system.

The functions performed by a body system are more complex than those performed by the organs.

•A number of systems are found in complex organisms to carry out essential bodily functions, such as:- Ensure genetic diversity- Digest food- Eliminate wastes, etc.

•An organism is made up of different systems working effectively individually as well as together in a group.

nosetracheabronchuslungs

Respiratory system

Blood circulatory systemTakes in oxygen from the

surroundings. Releases carbon dioxide and water vapour into the surroundings.

Carries food, oxygen and water to various parts of the body and carries wastes away to be removed.

Muscular systemEnables

movement

Male reproductive systemProduces sperms for

reproduction

From Systems to Organisms• Different types of multicellular organisms are made up of different numbers and types of systems.

Heart muscle cell (a cell)

Heart muscle (a tissue)

A group of similar cells that are specialised to perform a certain function together to form a tissues.

The heart (an organ)

A group of specialised tissues that are gathered in a certain part of the body to perform a particular functions together to form an organ.

Circulatory system

Various organs that work together to perform a major function in the body to form a system.

Different systems work individually, but together, they make up the whole organism.

CCellsells

TTissuesissues

SSystemsystems

OOrgansrgans

OOrganismrganism

Simple Tissues: Cells of the same type work together to perform a specific function

Simple Tissues: Cells of the same type work together to perform a specific function Complex Tissues: Several types of cells work together to perform a specific function

Complex Tissues: Several types of cells work together to perform a specific function

Different tissues work together to perform a specific functionDifferent tissues work together to perform a specific function

Several organs working together for a common purposeSeveral organs working together for a common purpose

Various systems work together to form the organismVarious systems work together to form the organism