cells – the basic units of life

WHAT IS A CELL?

A cell is the basic unit of structure and function in organisms hence basic unit of life.

Cells differ in size, shape and in function.

A cell made up of smaller structures called organelles.

Two types of cellsProkaryotic or Eukaryotic cells. Only organisms of the domains Bacteria

and Archaea consist of prokaryotic cells – cells without a membrane bound nucleus.

Protists, fungi, animals and plants all consist of eukaryotic cells – cell with a membrane bound nucleus.

General structure of an animal cell as seen under a light microscope (called a micrograph)

Line diagram of a general animal cell

Micrograph of a general plant cell

Line diagram of a general plant cell

DIFFERENCES BETWEEN PLANT- AND ANIMAL CELL

PLANT CELL ANIMAL CELL

CELL WALL CELL MEMBRANE

CHLOROPLAST NO CHLOROPLAST

BIG IN PLANTS SMALL IN ANIMALS

CAN PHOTOSYNTHESIZE CANNOT PHOTOSYNTHESIZE

MAKE THEIR FOOD DEPENDENT ON PLANTS IN CASES OF FOOD

STRUCTURE AND FUNCTIONS OF THE DIFFERENT ORGANELLS OF CELLS

Chapter 6 p. 98 – 131

CELL WALL(ONLY IN PLANT CELLS)

Porous Varies in thickness Consist of pectin (elasticity), cellulose fibrils held

together with non-cellulose substances (hardens the cell when mature) and lignin (adds strength to cell especially in woody plants)

Cell wall is permeable and protects the inside of the cell.

Middle lamella (layer of adhesive substances) – holds the cells together

Plasmodesmata (pores) that connects the cytoplasm of the connecting cells – selectively permeable

CELL WALL WITH PLASMODESMATA AND INTERCELLULAR SPACES

CELL MEMBRANE/PLASMA- (ANIMAL- AND PLANT CELLS)Consist of 2

phospholipid layers and proteins in between.

The phospholipid layers are part hydrophillic and part hydrophobic

NUCLEUS +/- 5µm, largest organelle in

cell. Enclosed by a

nucleomembrane with nuclear pores. Function: Protection and add to selective permeability.

Filled with nucleoplasma, a nucleolus and chromatin. Function of chromatin: carries genetic material in the form of chromosomes.

Function of nucleolus: Produce r-RNA

MITOCHONDRION Consist of 2 membranes:

Outer – and a highly convoluted inner membrane- These folds are called cristae – they increase the surface area.

Filled with matrix called stroma that contains DNA and ribosomes.

Function: Produce energy in the form of ATP by means of cellular respiration

CHLOROPLAST (PLANT CELL ONLY) Enclosed by a double

membrane Filled with stroma and

thylakoids filled with chlorophyll arranged in groups called grana.

Ribosomes and starch grains in stroma.

Function: Photosynthesis

VACUOLE(Large in plant-, small in animal-)

Membranous sacFilled with cell sap.Causes turgor pressure in the

vacuole.Function: Stores various

substances, including waste.Helps with osmotic potential

of cell.

OTHER SMALLER ORGANELLESEndoplasmic Reticulum – Transport

system in cellRibosomes – Protein synthesisGolgi-apparatus – Make lysosomes and

acts as transport system.Lysosomes – Intracellular digestion.Plastids e.g.– Leucoplasts – Stores

starch - Chromoplast – gives

colour to flowers and fruit.* Centrioli – Mitosis in animal cells

PERMEABILITY OF THE CELL MEMBRANEThe cell membrane has the ability to

regulate transport molecules across its structure.

This function is essential to the cell’s existence.

The fluid mosaic model helps to explain how membranes regulate the cell’s molecular traffic.

MICROSCOPYThe microscope is an instrument designed to observe objects too small to be seen with the naked eye.

The human eye cannot distinguish objects much smaller than 0.1mm.

The microscope act as an extension of the eye, allowing one to see smaller objects.