WELCOME TO BIOLOGY CLASS

Chapter 2: Cell Structure and Cell Organisation2.1 Cell Structure and Function

A house is made up of individual bricks

bricks are the building blocks for a house

All living organisms are made up of individual cells

Cells are the building blocks for organisms

Cellular Components the basic unit of life

Surrounded by a plasma membrane acts as a boundary that separates the cell from its environment

The living components inside the cell is protoplasm – consists of the nucleus and the cytoplasm

Plant cells have a cell wall which completely surrounds the plasma membrane

The cytoplasm contains organelles

Organelles

Perform specific functions which enable the cell to function as a unit of life

Nucleus, mitochondria, chloroplasts, vacuoles, ribosomes, lysosomes, the Golgi apparatus, endoplasmic reticulum

Animal Cell

Plant Cell

Endoplasmic reticulum

Ribosomes

Mitochondrion

Nucleus

Plasma membrane

Golgi apparatus

Centriole

Chloroplast

Vacuole

Cell wall

Cell Membrane Refers to all membranes found inside the cell

Plasma membrane – the membrane at the surface which encloses the content of a cell

Made of proteins and phospholipids

Semi-permeable membrane and acts as a selective barrier

Regulates the movement of substances into and out of the cytoplasm

Cell Wall A rigid outer layer that surround the plasma

membrane of a plant cell Composed of cellulose, a tough and fibrous

carbohydrate Permeable to all fluids – has tiny pores that

allow substances to move freely into and out of the cell

Gives shape and provide mechanical support Protects the plant cell from rupturing due to

the excessive intake of water

Cytoplasm

The region between the nucleus and the plasma membrane

Consists of a jelly-like matrix which the organelles are suspended

Contains organic and inorganic substances

Acts as a medium for biochemical reactions

Provides substances obtained from the external environment to the organelles

Nucleus

The largest organelle in the cell

Enclosed by a nuclear membrane

Contains the nucleoplasm and nucleolus

Chromosomes in the form of chromatin contained within the nucleoplasm

Carry genetic information and controls all the activities of the cell

Vacuole Fluid-filled sac – surrounded by tonoplast The fluid contained is called cell sap Typical plant cell – large central vacuole Young plant cell – numerous smaller vacuoles Act as a storage place in a cell Cell sap contains water, organic acids,

sugars, amino acids, mineral salts, waste substances, pigments and metabolic by-products

Cell sap supports herbaceous plants – do not wilt easily

Exists as large vacuoles in plant cells and feature temporarily or none at all in animal cells

Mitochondria

Cylindrical-shaped organelles

Involved in cellular respiration

Releases energy when food substances are broken down with the help of enzymes in the mitochondria

Energy released is stored in the form of ATP (adenosine triphosphates) – readily used by cells

Ribosomes Found attached to the surface of rough endoplasmic reticulum or

suspended freely in the cytoplasm

Each ribosome consists of two sub-units : one small and one large

Comprises a type of ribonucleic acid (RNA) and protein

Acts as a site of protein synthesis

Use information carried by the chromosomes to make the proteins

Endoplasmic Reticulum (ER) Consists of a network of folded membranes forming interconnected

tubules or sacs

The membrane is physically continuous with the nuclear membrane

Two types:

1) rough ER – has ribosomes attached to its surface

2)smooth ER – does not have ribosomes attached to its surface

Most of the biochemical reactions of the cell take place on these membranes

Rough ER Transports proteins made by ribosomes

Proteins that depart from rough ER are enclosed in vesicles

These proteins can be transported from one part of the cell to another

Smooth ER Is the site of important metabolic reactions including synthesis of

lipids and detoxification of drugs

Golgi Apparatus (GA)

Consists of a stack of flattened membranous sacs

Function as a processing, packaging and transporting centre of carbohydrates, proteins, phospholipids and glycoproteins

Rough endoplasmic reticulum

Plasma membran

e

Vesicle bud off and travel to the plasma membrane

Golgi apparatus

Transport Vesicle carrying proteins

Nucleus

Fuse and empty their contents

Modify proteins, sort and package them into vesicles

Proteins are released outside the cell

Lysosomes

Membrane-bound sacs contain hydrolytic enzymes (digest or break down complex organic molecules (proteins, lipids, polysaccharides and nucleic acids)

Also eliminate worn out mitochondria and other damaged organelles to enable a cell to renew itself

Centrioles

A pair of cylindrical structures located outside the nucleus

Composed of a complex arrangement of microtubules

Form a spindle fibres during cell division in animal cell

Not present in plant cells

Chloroplast

Typically lens-shaped

Contains the green pigment chlorophyll

It traps sunlight and convert light energy into chemical energy during photosynthesis

The green colour of plants comes from chlorophyll

Assessment1) Which of the following cellular components is found only in plant

cells?

Cell wall

Plasma membrane

Endoplasmic reticulum

Golgi apparatus

A

C

D

B

Congratulations! Congratulations!

Sorry…..Try again

2) Cellular respiration takes place in the

chloroplast

Golgi apparatus

centrioles

mitochondria

A

C

D

B

Congratulations! Congratulations!

Sorry…..Try again

3) Which of the following processes takes place in the organelle shown in photograph 1?

Respiration

Photosynthesis

Protein synthesis

Lipid synthesisA

C

D

B

Congratulations! Congratulations!

Sorry…..Try again