Table of Contents
- 2.1.1 Cell Structure
- 2.1.2 – Organization of Cells
- 2.1.3 Magnification Formula
- 2.1.4 Converting Between Units: Extended
2.1.1 Cell Structure
Animal & Plant Cells
Animals
- Main features of animal cells:
- They are multicellular
- They contain a nucleus with a distinct membrane
- They do not have cell walls
- They do not contain chloroplasts thus they are unable to carry out photosynthesis
- They feed on organic substances made by other living things
- They often store carbohydrates as glycogen
- They usually have nervous coordination
- They are able to move from place to place
Plants
- The main features of plant cells:
- They are multicellular
- They contain a nucleus with a distinct membrane
- They have cell walls made out of cellulose
- They contain chloroplasts, which means they can carry out photosynthesis
- They feed by photosynthesis
- They store carbohydrates as starch or sucrose
- They do not have nervous coordination
| Structure | Function |
| Nucleus | Stores the genetic material (known as DNA) which controls and regulates the activities of the cell |
| Cytoplasm | Gel-like substance mainly composed of water and dissolved solutes Supports the internal cell Site of chemical reactions, which also includes anaerobic respiration |
| Cell membrane | Holds the cell together Controls which substances can enter and leave the cell |
| Ribosomes | Found in the cytoplasm Site of protein synthesis |
| Mitochondria | Known as the “powerhouse of the cell” Site of most reactions, involved in aerobic respiration, where energy must be released in order to fuel cell processes. |
| Structure | Function |
| Cell wall | Made of cellulose Gives the cell extra support |
| Chloroplasts | Contains chlorophyll to absorb sunlight and enzymes needed to photosynthesize |
| Vacuole | Contains the cell “sap” Used for storage of materials Also helps support the shape of the cell |
Bacteria Cells
- Bacteria, which have a wide variety of shapes and sizes, all share the following biological characteristics:
- They are microscopic single-celled organisms
- They possess a cell wall, cell membrane, cytoplasm and ribosomes
- They lack a nucleus but contain a circular chromosome of DNA that floats around in the cytoplasm
- Plasmids are also sometimes present. Plasmids are small rings of DNA that contain extra genes to those found in the chromosomal DNA
- They lack mitochondria, chloroplasts and other membrane-bound organelles found in animal and plant cells
- Some bacteria also have a flagellum or flagella (plural). These are long, thin, whip-like tails attached to bacteria that allow them to move
Identifying Cell Structures & Function
- Within the cytoplasm, the following organelles are visible in almost all cells except prokaryotes when looking at higher magnification:
- Mitochondria are organelles found throughout the cytoplasm
- Ribosomes are tiny structures that can be free within the cytoplasm or attached to membranes within the cell known as the endoplasmic reticulum.
- Endoplasmic reticulum studded with ribosomes looks rough under the microscope; this gives rise to its name of rough endoplasmic reticulum.
- Vesicles can also be seen using a higher magnification – these are small circular structures found moving throughout the cytoplasm
2.1.2 – Organization of Cells
Producing New Cells
- The ones in your body need to be able to divide to help your body grow and repair itself
- They grow and divide over and over again
- New cells are produced by the division of existing ones
Specialized Cells
- This type of cell are those which have developed certain characteristics in order to perform particular functions. These differences are controlled by genes in the nucleus
- Cells specialize by undergoing differentiation: this is a process by which cells develop the structure and characteristics needed to be able to carry out their function
| Cell | Function | Adaptation |
| Ciliated cell | Controls the movement of mucus in the trachea and/or bronchi | Hair-like structure called cilia that beat to transport the mucus and trapped particles to the throat |
| Nerve cell | Transmit signals in the form of electrical impulses | Long Has extensions and branches, so it can communicate with other nerves, muscles, etc |
| Red blood cell | Transports oxygen through the blood | Biconcave shape, which helps to increase surface area so that oxygen can be transported more easily Contains hemoglobin which combines with oxygen to transport it Contains no nucleus so there is more space for hemoglobin |
| Sperm cell | Reproduction (fertilize the egg cell) | Head contains genetic material Acrosome in the head contains digestive enzymes so it can penetrate the egg cell and fertilize Mid-piece contains mitochondria, provides energy to the head to penetrate the egg, and the tail to swim. Tail enables the sperm to swim |
| Egg cell | Reproduction | Contains lots of cytoplasm Nucleus contains genetic information Cell membrane changes after it has been fertilized by sperm so that no more can enter. |
| Cell | Function | Adaptation |
| Root hair cell | Absorbs water and minerals from soil | Root hair increases the surface area of the cell to ensure maximum absorption of nutrients. Walls are thin to ensure water transports quickly. |
| Xylem vessel | Supports the plant | No top and bottom walls, so water can continuously flow freely The side walls thicken with the help of lignin so they can help support the plant |
| Palisade mesophyll cell | Responsible for photosynthesis | Shaped like a column to maximize the absorption of sunlight Contains lots of chloroplasts for maximum photosynthesis |
Levels of Organization in an Organism
| Level | Description |
| Cells | Basic functioning and structural unit of life |
| Tissues | Group of similar-structured cells working together to perform the same function |
| Organ | Made from different tissues working together to perform specific functions |
| Organ Systems | Group of organs with relating functions, working together to perform bodily functions |
2.1.3 Magnification Formula
- Magnification is calculated using the following equation:
Magnification = Image size ÷ Actual size
An easy way to remember it is by drawing this triangle:
Rearrange the equation however you like depending on the question that you receive.
Keep this in mind:
- Magnification = image size / actual size
- Actual size = image size / magnification
- Image size = magnification x actual size
- ALWAYS LOOK AT THE UNITS!
- LEARN THE TRIANGLE SO YOU CAN DRAW IT IMMEDIATELY ON YOUR PAPER!
- MAGNIFICATION HAS NO UNITS
2.1.4 Converting Between Units: Extended
Conversion table (centimeter to millimeter to micrometer):
And that’s it for Topic 2! Hope this revision guide will help you to ace your exams!
If you want to check out the Topic 1 Revision Guide, click this link here!
If you’d like to watch a video regarding this topic, click this link here!
English