B1 Cell structure and transport

B1.1 The world of the microscope

The first light microscopes were developed in the mid 17th century and they are used to look at cells. They use a beam of light to form an image and magnify. They are cheap.

The electron microscope in 1930 allowed understanding about subcellular structures in the cells. Transmission electron microscopes give 2D images with high magnification and resolution. Scanning electron microscopes give 3D images but lower magnifications. They are expensive.

To calculate magnification, multiply the magnification of they eyepiece lens and the magnification of the objective lens.

To calculate the size of objects under the microscope:

magnification = size of image / size of real object

Microscopes are useful due to magnification but there is a minimum distance between two objects when you can see them clearly as two separate things but if closer, they may appear as one object (resolution). The resolving power of the microscope affects how much it can show.

B1.2 Animal and plant cells

The nucleus controls all the activities of the cell and contains the genes on the chromosomes carrying the instructions for making proteins needed to build new cells or organisms.

Organelles are suspended in the cytoplasm and it is where most of the cell reactions occur.

The cell membrane controls the passage of substances and their movement.

The mitochondria are structures in the cytoplasm where aerobic respiration occurs releasing energy.

The ribosomes are where protein synthesis occurs, making proteins needed for the cell.

Plant cells make their own food by photosynthesis. Plant cells contain the features of an animal cell but other features needed for their function.

Algae are simple aquatic organisms classed as protista.

Plant and algal cells have a cell wall made of cellulose strengthening an supporting the cell.

They also have chloroplasts which contains chlorophyll that absorbs light for photosynthesis. A permanent vacuole is a space in the cytoplasm filled with sap for keeping the cells rigid to support the plant.

Required practical: set up a microscope and observe, draw, and label cells. Follow safety procedures if you are setting up your own cells.

B1.3 Eukaryotic and prokaryotic cells

Animal and plant cells are eukaryotic cells - cells having a cell membrane, cytoplasm, and genetic material enclosed in the nucleus. The genetic material is DNA forming structures called chromosomes contained within the nucleus.

Bacteria are single celled living organisms. They have a cytoplasm and cell membrane but the cell wall doesn't have cellulose. In prokaryotic cells the genetic material is not in the nucleus; it is a single DNA loop found free in the cytoplasm. There may also be small extra rings of DNA (plasmids) which code for very specific features. Some have a protective slime capsule outside the cell wall and some have flagellum, a long protein strand used to move around.

Orders of magnitude - used to make approximate comparisons between things shown by using powers of 10. If something is 10x bigger than something else, it is an order of magnitude…