Cell Biology - Cell Structures

Fundamentals of Cell Biology

Cells serve as the fundamental building blocks of every organism on the planet.
All living things are composed of cells.
Cells are categorized into two primary types: Prokaryotic and Eukaryotic. * Eukaryotic Cells: These are complex cells. All animal and plant cells fall into the eukaryotic category. * Prokaryotic Cells: These are smaller and simpler cells. Bacteria are the primary example of prokaryotic cells.

Subcellular Structures of Animal Cells

Subcellular structures refer to the different parts that make up a cell. Most animal cells contain the following structures:

Nucleus: This structure contains the genetic material of the cell. The genetic material is responsible for controlling the activities and functions of the cell (Note: See page 61 for further details on genetic material).
Cytoplasm: A jelly-like substance where most of the chemical reactions within the cell take place.
Ribosomes: These serve as the site where proteins are manufactured within the cell.
Cell Membrane: This structure surrounds the cell and controls the movement of substances in and out of the cell.
Mitochondria: This is the site where aerobic respiration occurs. Respiration is critical as it transfers the energy that the cell requires to function effectively (Note: See page 48 for further details on respiration).

Subcellular Structures of Plant Cells and Algae

Plant cells typically contain all the subcellular structures found in animal cells (nucleus, cytoplasm, ribosomes, cell membrane, and mitochondria), but they also possess additional specialized structures:

Cell Wall: A rigid structure made of cellulose that surrounds the cell membrane. Its primary function is to support and strengthen the cell.
Permanent Vacuole: A space in the cytoplasm filled with cell sap.
Chloroplasts: The site where photosynthesis occurs. Photosynthesis is the process that produces food for the plant (Note: See page 44 for further details on photosynthesis).
Algae (e.g., Seaweed): The cells of algae also possess a rigid cell wall and chloroplasts similar to plant cells.

Subcellular Structures of Bacterial Cells

Bacterial cells are prokaryotic and have a distinct organization compared to eukaryotic plant and animal cells:

Cell Wall: Provides structure to the bacteria.
Cell Membrane: Controls the passage of materials.
Cytoplasm: The site of internal cellular activity.
Single Loop of DNA: Bacteria do not possess a 'true' nucleus; instead, their genetic material is found in a single circular loop of DNA.
Plasmids: These are small, additional rings of extra DNA found within the bacterial cell.

Mathematical Estimations and Skills in Cell Biology

To understand cells, one must be able to calculate and describe their physical dimensions.

Estimating the Area of a Subcellular Structure

To estimate the area of a subcellular structure, it should be treated as a regular geometric shape.

Example: Estimating Mitochondrion Area * A mitochondrion (singular of mitochondria) can be approximated as a rectangle. * The formula for the area of a rectangle is: $\text{Area} = \text{length} \times \text{width}$ . * If a mitochondrion has a length of $10\,\mu m$ and a width of $1\,\mu m$ , the calculation is as follows: * $\text{Area} \approx 10\,\mu m \times 1\,\mu m = 10\,\mu m^{2}$ .

Maths Foundations

Standard Form: In examinations, the sizes of cells are frequently written in standard form. This is a method of writing very large or very small numbers using powers of $10$ .

Questions & Discussion

Question 1 (Q1): Give two differences in structure between bacterial cells and animal cells. [2 marks]

Potential Answer Points: 1. Bacterial cells have a cell wall, whereas animal cells do not. 2. Bacterial cells have a single loop of DNA instead of a true nucleus, while animal cells have a nucleus. 3. Bacterial cells may contain plasmids (small rings of DNA), which are absent in animal cells.