Biology Landmark 1 Notes

Prokaryotes

• Organisms are single-celled
• Contain cytoplasm
• Have a cell membrane
• DNA is a single loop or several small rings 
• No organised membrane-bound nucleus
• Very small

Eukaryotes

• Organisms are multi-cellular
• Have a cell membrane
• DNA contained within membrane-bound nucleus
• Contain cytoplasm

Red blood cell - is biconcave and has no nucleus to maximise surface area

Ciliated cell - moves mucus - has flagella to help push mucus along

Root hair cell - absorbs water and minerals - large surface area, thin walls

Muscle cell -  enables movement - contracts and expands to allow movement

Palisade cell - collects sun for photosynthesis - big surface area + chloroplasts.

Nerve cell - transmits electrical signals - long and thin to reach all parts of the body.

Magnification = measured size/ actual size

Resolution - The amount of detail that can be seen

Light microscopes: Light and mirrors are used. Can see things much smaller than with the naked eye, for example a human sperm cell, but nothing smaller than the wavelength of light.

Electron microscopes: Can see in a lot of detail, and much smaller things than light microscopes (e.g blood clots). They are non-intrusive.

Transmission electron microscopes: Can see in very high resolution and can see inside cells so we can look at organelles. However, using a transmission electron microscope might damage specimens...

Mitosis is the process of cells dividing to form new cells. During this process, chromosomes separate and the whole cell divides...

The Process of Mitosis

1. Numbers of organelles increase

2. A complete set of chromosomes goes to each end of the cell and forms two new nuclei

3. The cytoplasm divides to form two identical cells!

Diffusion is the passive overall movement of particles from a region of high concentration to a region of low concentration down a concentration gradient.

Osmosis is the diffusion of water molecules through a partially permeable membrane, down a concentration gradient.