B1: Cell structure and transport

Units

• 1km = 1,000 m
• 1m = 100 cm
• 1cm = 10 mm
• 1mm = 1,000 um (micrometers)
• 1um = 1000 nm (nanometers)

Types of microscopes 

• Light microscopes are cheap but can't magnify as far. They magnify up to x2000 and were first developed in the early 17th century.
• Electron microscopes are more expensive but have a higher resolution and magnification (up to x2,000,000) and therefore have more detail. They were first developed in the 1930's.

Equation 

magnification = size of image/size of real object

Organelle:

• Cell membrane - controls the passage of substances (like glucose) into the cell and substances (like urea and hormones) out of the cell
• Cytoplasm - a liquid gel were other organelles are and is where chemical reactions (like anaerobic respiration) needed for life take place
• Nucleus - controls the activities of the cell. It is surrounded by the nuclear membrane and contains genes that carry out instructions for making proteins that build new cells
• Ribosomes - where protein synthesis takes place and makes all the proteins needed in the cell
• Mitochondria - aerobic respiration takes place here which gives the cell energy. It also structures the cytoplasm

see textbook for a diagram :)

Organelles: (only found in plant cells)

• Cell wall - made from cellulose, strengthens the cell and gives it support
• Choroplasts - contain chlorophyll which absorbs light for photosynthesis and makes plants green
• Vacuole - a space in the cytoplasm filled with sap that supports the structure of the cell

see textbook for diagram :)

What are they?

These are cells found in organisms such as bacteria and archaea that are very simple. These cells have their genetic material in the cytoplasm and on rings called plasmids- not in a nucleus.

Key facts:

Size: 0.2um - 2.0um

Outer layers of cell: cell membrane- surrounded by cell wall

Cell contents: cytoplas, ribonsomes, no mitochondria or chloroplasts 

Genetic material:  DNA is a single molecule, found in the cytoplasm - additional DNA is found on one or more rings called plasmids

Type of cell division: Binary fission 

What are they?

They are complex cells, found in animals, plants and fungi. These cells have their genetic material in a nucleu.

Key facts:

Size: 5up- 100up

Outer layer of cells: cell membrane- surrounded by cell wall in plants and fungi

Cell contents: cytoplasm, cell organelles include mitochondria, chloroplasts in plants and ribosomes

Genetic material: DNA in a nucleus- plasmids are found in a few simple eukaryotic organisms

Type of cell division: mitosis

Sperm cells

• A large nucleus contains the genetic information to be passed on
• A long tail helps the sperm swim through the female reproductive system
• Lots of mitochondria which gives the cell energy needed to swim
• The acrosome stores digestive enzymes used for breaking the outer layers of the egg

Nerve cells

• Specialised to carry electrical pulses around the body of an animal
• Provide a rapid communication system between the parts of the body
• Lots of dendrites make connections to other nerve cells
• An axon carries the nerve pulse around the body (the longest runs from the foot to the spine)

Muscle cells

• Contain special proteins to allow contractions
• Contain many mitochondria to release energy
• Can store glycogen, broken down in respiration 

Root hair cells

• They have a large surface area to absorb water from soil 
• A large vacuole helping water movement by osmosis 
• Many mitochondria to provide energy for active transport in cells

Xylem cells

• Xylem is the transport tissue in plants that carries water and mineral oils from the roots to the highest leaves and shoots
• They die to form long hollow tubes for the movement of water and mineral ions up the plant
• Lignin lines their walls, making them strong, waterproof and giving the plant support

Phloem cells

• Phloem is the specialised transport tissue that carries the food made by photosynthesis around the body of the plant
• They have companion cells supporting them as they have lost lots of their organelles
• Cell walls between cells break down to form sieve plates, so dissolved food can flow easily

Definition: Diffusion is the spreading out of particles of any substance in solution or gas, resulting in a net (overal) movement from an area of higher concentration to an area of lower concentration, down a concentration gradient.