Cell Structure & Organisation
Four Structural levels of the body:
Cells - most basic structural and function unit of living organsims. Eg, red blood cells transport oxygen throughout body
Tissues - group of similar cells that work together to carry out a particular function. Eg, muscles
Organ - two or more types of tissue working together to form a particular task. Eg, heart muscles working together to beat heart.
System - group of organs that work together to carry out a particular task, necessary for survival. Eg, digestive system
Organism - all body systems working together to meet the needs of a functioning organism.
Structure & Function of Organelles:
Cell Membrane -
→ Outer boundary of cell, separates cell contents from environment outside and from neighbouring cells.
→ Made up of double layer of lipids and associated proteins
→ Semi- permeable membrane - meaning determines what substances can enter and exit the cell
Cytoplasm -
→ Thick jelly like fluid within the membrane that suspends structures in it.
Cytosol -
→ thick jelly like fluid
→ 75% - 90% of water mixture of dissolved substances (salts & carbs) and non-soluble substances (proteins & fats) suspend in fluid.
→ location of metabolic rates
→ Controls osmotic pressure and flow of chemicals in and out of cell.
Cytoskeleton -
→ Framework of protein fibres giving cells shape and assisting movement;
Microtubules - hollow rods keeping organelles in place/moving around the cell.
Microfilaments - move materials around cytoplasm or move whole cell
Nucleus -
→ Nuclear membrane that separates nucleus form cytoplasm.
Double membrane
Nuclear pores - allow large molecules (RNA) to enter and leave the nucleus
→ Controls the structure and function of the cell via DNA
Nucleolus -
→ Manufactures proteins
→ contains mainly RNA
→ DNA and nucleolus are suspended in jelly-like nucleoplasm
Endoplasmic Reticulum -
→ Pair of parallel membranes extending through the cell from nucleus to membrane - channels created by these are ER
→ Provides surface area for chemical reactions and channels for supporting, synthesising, storing and transporting molecules.
Ribosomes -
→ very small, spherical organelles.
→ site at which amino acids join to make proteins
→ free in cytoplasm or joined to ER = RER
Golgi Body -
→ Series of flattened stacks of membranes - usually near nucleus.
→ Proteins produced by ribosomes travel through ER channels to the Golgi Body where they are modifies and packaged into vesicles from secretion of the cell.
Lysosomes -
→ Small spheres bound by a membrane and formed by Golgi Body.
→ Contain digestive enzymes that break down large molecules ( proteins + lipids + carbs).
→ Particles/liquids entering the cell form vesicles - lysosomes can join with vesicles and break down the contents through digestive enzymes.
→ Also can breakdown worn out organelles.
Mitochondria -
→ sausage shaped organelles spread through out cytoplasm.
→ Double membrane - smooth outer membrane + folded inner membrane called cristae.
folded membrane creates a large surface area, therefore increasing chemical reactions such as cellular respiration.
Some cells have a high amount of mitochondria due to their function and how much ATP is needed for that particular cell. Some cells are busier due to their increase in chemical reaction.
→ Site of cellular respiration thus making energy (ATP) for cellular activity.
Cilia and Flagella -
→ fine projections that beat back and forth
→ short - cilia
→ long - flagella
Centrioles -
→ pair of cylindrical substances, near nucleus
→ Reproduction of cell via cell division through forming spindle fibres.
Inclusions -
→ chemical substances that aren’t part of cell structure but found in cytoplasm. Eg, melanin.
Surface Area of a Cell:
→ As a cell grows, the volume of the cell increases.
→ the greater the volume of the cell the greater its need for energy, nutrients and gases and the more wastes it will produce.
→ The surface area to volume ratio is the comparison between the outer surface area and the inner volume.
→ The SA:VOL ratio decreases as the size of an object increases, meaning smaller objects have a higher ratio than larger ones.
→ Cells need to have a high SA:VOL ratio as this means the cells can easily exchange materials needed for vital metabolic processes and stay alive.
→ A small cell is more efficient as there is a higher SA:VOL ratio as materials/substances can be diffused quicker into the cell.