2.1 Cell Structure and Organisation

Organelles: internal membrane bound structures in cells that perform specific functions.
Organelles are surrounded by a single or double membrane.

1. Cell Membrane: protects the cell and control what enters and leave the cell

Partially permeable
Composed of lipid bilayer made of phospholipid molecules, a very thin layer of protein & fat
Proteins help materials move in and out of the cell
Some carbohydrate chains attached to proteins serve as chemical signals to help cells recognize each other or for hormones or viruses to attach

2. Cell Wall: protects and supports the cell... prevents it from bursting

Fully permeable
Plant cell wall made of cellulose , Fungal cell wall made of chitin , Bacteria cell wall made of murein or peptidoglycan

3. Cytoplasm: site of metabolic reaction

4. Nucleus: controls all activities of the cell , stores genetic info in DNA to make proteins

Surrounded by a double layer called the nuclear envelope containing pores
Chromatin is the long strand of DNA in the nucleus, which coils and become short and thick during cell division to make chromosomes.
Chromosomes contains information which is inherited from the parents to their offspring’s. They contain a string of genes. Genes are a length of DNA that codes for a specific protein.
Nucleolus inside the nucleus makes ribosomes and RNA. It disappears during cell division.

5. Chloroplast: site of photosynthesis , contains a green pigment called chlorophyll

Contains starch grains
Double membrane organelle with an inner system of membranous sacs called thylakoids, containing chlorophyll. Each stack of thylakoids is called Granum.

6. Mitochondria: site of aerobic respiration

Double membranes.. outer is smooth and inner has folds called cristae
Breaks down energy in glucose to ATP for cell use
Stores glycogen granules – Glycogen is the reserve fuel that it breaks down when needed
Cells with high rates of metabolism require large numbers of mitochondria to provide sufficient energy
Have their own DNA to make more when needed

7. Vacuoles: serves as a storage area for proteins, ions, wastes, and cell products

Plant cells have large, permanent vacuoles containing cell sap (solution of sugars and other products).. many contain poisons to keep animals away
A full vacuole creates turgor pressure keeping cell firm and turgid
Animal cells have small, temporary vacuole. They’ve smaller membrane bound spaces called vesicles which may contain food or water

8. Lysosomes: also called suicidal bags

Contain hydrolytic enzymes to digest materials
Lysosome vesicles are formed from sacs that pinch off from the ends of Golgi (organelle that modifies, packages, & helps secrete cell products such as proteins and hormones. It receives products made by the ER )

9. Endoplasmic Reticulum (ER): site of protein synthesis

Proteins are made by joining amino acids together in a long chain. Proteins are made based on the instructions carried on the DNA in cell’s nucleus that specify the sequence of amino acids that should be joined together to make a particular protein.
Membranous tubules and sacs that transport molecules from one part of the cell to another, also connects nucleus with cell membrane
May be free in cytoplasm or attached to RER
Rough ER has embedded ribosomes on its surfaces for making proteins
Smooth ER lacks ribosomes and helps to make lipids and fats
Ribosomes are not organelles

	Created by Alisar Younes almost 7 years ago

IGCSE Biology Note on Unit 2. Organisation of the Organism, created by Alisar Younes on 20/11/2017.

Unit 2. Organisation of the Organism