2.8+Cells


1. Every living organism is made of one or more cells.  2. The cell is the basic unit of structure and function. It is the smallest unit that can perform life functions.

3. All cells arise from pre-existing cells.

Prokaryotes
Prokaryotes are very simple cells, probably first to inhabit the earth. Prokaryotic cells do not contain a membrane bound nucleus. Bacteria are prokaryotes. DNA of bacteria is circular. The word "prokaryote" means "before the nucleus"

Eukaryotes
 Eukaryotic cells are more advanced cells. These cells are found in plants, animals, and protists. The word "Eu" means "true" and "karyotes" means "nucleus. Hence Eukaryotes have a true nucleus. The eukaryotic cell is composed of 4 main parts:

 **cell membrane** - outer boundary of the cell
 * cytoplasm** - jelly-like fluid interior of the cell
 * nucleus** - the "control center" of the cell, contains the cell's DNA (chromosomes)
 * organelles** - "little organs" that carry out cell functions

Both plant cells and animal cells are eukaryotic.

[|www.biologycorner.com/ bio1/cell.html]

ANIMAL CELL
Below is an example of an animal cell.



PLANT CELL
Below is a picture of a typical plant cell. Can you see any differences between the plant and animal cell?

SPECIALISED CELLS

A cell that has altered so it can perform a specific function in a multicellular organism.

Animal cells are often specialised so that they can carry out a particular function.

<span style="font-size: 110%; font-family: 'Comic Sans MS', cursive;">1) The sperm cell - designed to fertilise eggs A sperm cell is very small and has a little tail which provides movement so it can swim and find an egg to fertilise Its head contains enzymes (in the vacuole) which allow it to digest its way through an egg membrane so the two nuclei can join It contains half the number of chromosomes in the nucleus - these carry genetic information from the father, which will be passed on to the offspring

<span style="font-size: 110%; font-family: 'Comic Sans MS', cursive;">2) The ovum (egg) cell - designed to be fertilised An ovum is large and bulky because no active movement is needed - it just sits and waits for the sperm to find it It contains yolk (in the cytoplasm) which provides a large food store needed for the developing young organism once it's fertilised It contains half the number of chromosomes, which carry genetic information from the mother - this will be passed on to the offspring.



<span style="font-size: 110%; font-family: 'Comic Sans MS', cursive;">3) The palisade cell - designed for photosynthesis A palisade cell is tall with a large surface area It's found on the top side of a leaf - ideal for good absorption of carbon dioxide and light - both are needed for photosynthesis They're packed with chloroplasts, which contain the green pigment chlorophyll, which is needed for photosynthesis



<span style="font-size: 110%; font-family: 'Comic Sans MS', cursive;"> 4) The cilia cell - designed to stop lung damage Cilia cells line all the air passages in your lungs They have tiny hairs, which filter the air as it blows through The hairs sweep mucus (snot) with trapped dust and bacteria up to the back of the throat where it is swallowed



<span style="font-size: 110%; font-family: 'Comic Sans MS', cursive;">5) The root hair cell - designed for absorbing The long hair cell increases the surface area of the root, which helps absorption of water and minerals It has a really thin cell wall, which makes it easier for minerals to pass across into the root itself