Cell Structure and Organisation

Key Question: What is life made of?

Life generally consists of : ability to move, ability to reproduce and ability to take in use nutrients for its growth

Learning Outcomes

• Identify the main organelles and membranes in the cell (nucleus, mitochondria, cell surface membrane, cytoplasm, Golgi Apparatus, endoplasmic reticulum, cell wall, chloroplast, vacuole)

• Explain the various functions of different organelles

Learning Outcomes

• Compare the structure of plant and animal cells

• Describe the relationship between structure and function as seen in xylem vessels, root hair cells and red blood cells

• Differentiate between the levels of organisation in an organism

The term “cell” was first introduced by Robert Hooke in 1667 who examined thin slices of cork under a microscope

Cork cells (dead plant cells) as seen by Robert Hooke

What is a cell?

Cell is the basic unit of structure and function in an organism

It is the basic block of life

All organisms are composed of one (unicellular) or more cell (multicellular)

What is a cell?

A cell is like a factory. What do you think are the parts or functions of a factory that may be similar to the cell?

How do we study the parts of a cell?

• Use of microscopes-> light microscope (magnifies objects up to 1000x)-> electron microscope (magnifies objects to >200,000x)

Structure of the cellProtoplasm: •Each living cell consists of living material called protoplasm which is contained within the cell membrane.

•The protoplasm is made up of 70% water and 30% of other substances, most of which are proteins, carbohydrates and fats.

•The composition of protoplasm varies greatly from cell to cell.

Diagram of animal cell

Diagram of animal cell

Diagrams of plant cell

Both Cells

Cell surface Membrane (plasma membrane)

Thin partially permeable membrane that surrounds the cytoplasm

Controls substances entering or leaving cell

Keeps cell content in placePPM is like a door that allows only some substances to cross it.

Cytoplasm: Is the part of the protoplasm between the cell surface membrane and the nucleus

Contains enzymes and a suspension of specialised structures called organelles

Site within cell in which most cell activities occur

Both Cells

(cytoplasm)

Organelles carry out various functions in the cell.

Nucleus:Small spherical structure consisting of nucleoplasm surrounded by a nuclear envelopeContains one or more nucleoli and chromatin

Both Cells

Nucleoplasm

Functions of the nucleus:

Controls cell activities such as growth and repair of worn-out parts

Involved in cell division

Functions of the nucleolusNucleolus: needed to

make ribosomes

Both Cells

Chromatin:

Network of long thread-like structures that control cell division

Each chromatin thread is made up of proteins and deoxyribonucleic acid (DNA)

Chromatin threads condense to become chromosomes (highly coiled structures) during cell division

Both Cells

Organelles- Endoplasmic reticulum (ER)• There are 2 types of ER – rough ER and smooth

ER.

Both Cells

Rough Endoplasmic reticulum (RER)• Outer surface appears rough and is

continuous with nuclear envelope

• Ribosomes attached to outer surface

• RER transports proteins made by ribosomes to Golgi apparatus for secretion out of cell

Both Cells

Smooth Endoplasmic reticulum (SER)• More tubular and may or may not be connected to RER

synthesises substances such as lipids and steroids (sex hormones)converts harmful substances into harmless materials (detoxification)

Both Cells

Golgi apparatus (Golgi body)

• Shaped like a disc• Consists of stack of flattened

spaces surrounded by membrane

• Vesicles can be seen fusing with one side of Golgi apparatus and pinching off on opposite side

• Golgi apparatus-> stores and modifies

substances made by ER (both SER and RER)

-> packages these substances in vesicles for secretion out of cell

Both Cells

Are vesicles the same as

vacuoles?

Vesicles or vacuoles

• a vesicle is a relatively small intracellular, membrane-enclosed sac that stores or transports substances.

• Vacuoles store food and other materials needed by a cell.

Mitochondrion

Sausage-shaped like organelles; double membrane with inner membrane thrown into deep folds called cristae

Both Cells

inner compartment

outer membrane

matrix

cristae

Mitochondrion…• Site of aerobic respiration to release energy Site of aerobic respiration to release energy

from food used by cell for growth and from food used by cell for growth and reproductionreproduction

• During aerobic respiration, food substances are broken down to their molecules to release energy.

• This energy may be used by the cell to perform cell activities such as growth and reproduction.

Vacuoles

• Fluid filled spaced enclosed by membrane

• Store substances with cell

• Animal cell: many small vacuoles that contain water, food substances and enzymes- (digestive enzymes to digest invading bacteria); usually exist temporarily

vacuoles

Vacuoles

• Plant cell: large central vacuole containing cell sap (nutrients- sugars, amino acids, mineral salts, wastes, poisonous substances that deter animals from feeding on plant parts) enclosed by a tonoplast (partially permeable)

Cell Wall:

Rigid wall made of celluloseCell wall is fully permeable

Protects the cell from injury and gives plant cell a fixed shape

Plant Cell

lysosome

plasma membrane

cell wall

nucleolus

nucleus

mitochondrion

sap vacuole

chloroplast

cell wall of adjacent cell

Chloroplasts:

Oval structures

Contain a green pigment called chlorophyll

Carry out photosynthesis

Plant Cell

Centrioles

• Cylindrical structures that exist as a pair

• Plays a role in cell division

Differences between plant and animal cells

Feature Plant Cell Animal Cell

Cell Wall Present Absent

Vacuoles A single, large central vacuole

Vacuoles are small and many (temporary)

Chloroplasts Present in photosynthetic cells

Absent

Centrioles Absent Present

Specialized Cells, Tissues, Organs and Systems

There are many different groups of cells which have different structure, shapes and sizes

They are adapted to perform specific roles

Differentiation:- A process by which a cell becomes specialised for a specific function

Examples: Root hair cells Red blood cells Xylem vessels

Relating structure to function

Red blood cellRoot hair cellXylem vessel

Red Blood Cell – oxygen transport

No nucleus:- can carry more haemoglobin and thus more oxygen

Circular biconcave shape:

- Increase surface area to volume ratio of cell for diffusion of oxygen into and out at a faster rate

Contains haemoglobin:

-Combines with oxygen to form oxy-haemoglobin which transport oxygen from lungs to all parts of body

Root Hair Cell - absorption

Long and narrow protrusion of epidermal cell (root hair):

- increases surface area to volume ratio of cell so that water and mineral salts can be efficiently absorbed from the soil

The Xylem Vessel

xylem epidermis

phloem

cambium

xylem

thickened band

lumen

hollow vessel

long vessel

Transverse section through a dicotyledon stem to show the xylem

vessels

Xylem vessel

Dead Plant cells laid end to end (without nucleus and cytoplasm) with thickening cell walls Xylem vessels

Absence of cross walls or protoplasm

- enables water to move easily through the lumen

Long, hollow tubes formed from xylem cells laid end to end

- Allows water and

mineral salts to be

conducted from roots to

stem and leaves

Lignin deposited on walls of xylem vessels

- strengthens wall and prevents vessels from collapsing

Xylem Vessels – conduction and support

xylem vessels bundled together

- provides mechanical support to plant

Cell is the basic unit of structure and function in an organism

It is the basic block of life

From cells to tissues to organs to systems!

TissuesDefined as a group of similar cells working together to perform a specific function

There are simple tissues and complex tissues

Example of tissues:- Epithelial tissues- Connective tissue- Muscles tissue- Nervous tissue

Simple tissues (cells of the same type)

Animal tissues Plant tissuesEpithelial tissues

Epithelial tissues

These are sheets of cells which

cover the external surface or line the

cavities of the body

Muscle tissuesMuscle tissues

These are concerned with

body movements by contracting

epithelium lining blood

vessels

epithelium covering the

ovary

epithelium lining the trachea

muscles in the walls of the

intestine

muscles of the heart

Epidermis

Covering tissues of leaves and stems

Animal tissues Plant tissues

Complex tissues (several types of cells)

Connective tissuesConnective tissues

These join together body structures, providing protection and support

Nervous tissuesNervous tissues

These are concerned with the conduction of nerve impulses throughout the body

bloodnerve tissue of the brain

Vascular tissues-xylem and phloem tissue

OrgansA structure made of different types of tissues working together to perform specific functions

There is division of labour among the organs

Organs in animals

Stomach (store food, digest and churn)• glandular tissues secrete digestive juices• Muscular tissues causes stomach to contract

and mix food with digestive juices• Nervous tissue coordinates actions of stomach

Plant organsPlant organs

Leaves- Make food

Stem-transports water with dissolved mineral salts from roots to leaves and food from leaves to other plant parts- gives support to plant above ground

SystemsSeveral organs working together for a common purpose make up an organ system

Examples:- Digestive system

- Respiratory system- Nervous system- Circulatory system

small intestinelarge intestine

liver stomach

pancreasgall bladder

tonguesalivaryglands

oesophagus

rectum

Digestive system

From systems to organisms• The different systems in the body make up the

whole organism

Division of labour in cells

• In each cell, there are organelles specially designed to perform a specific job.

• For example: chloroplasts allow plant to make food, mitochondria enables respiration to take place...

• Division of labour (breakdown of workload to smaller and more specific tasks) helps individual cells function more efficiently

Division of Labour

SummaryFeatures Plant Cells Animal Cells

Nucleus √ √

Cell membrane √ √

Cytoplasm √ √

Mitochondria √ √

Endoplasmic Reticulum

√ √

Golgi Apparatus √ √

Cell Wall √ X

Chloroplasts √ X

Vacuole 1 large vacuole Numerous small vacuoles

Tonoplast √ X

Summary

Specialized Cells

Root hairs Red Blood Cells Xylem Vessels

Absorption of water & mineral salts

Transport oxygen Transport of water & mineral salts

Example

Function Function Function

* How are they adapted for their functions?

SummaryCells

Tissues

Organs

Systems

form

form

form

Organisms

form

Cell

Heart Organ

Cartilage Tissues

Organism