Define cell biology
This deals with cell structure, function and cell physiology all at the unit level of a living organism called a cell.
What is cytology?
The study of the structure of cells.
List the main functions of the cell (6 points)
- Basic unit of life.
The cell is the smallest part to which an organism can be reduced that still retains the characteristics of life.
- Protection and support.
Cells produce and secrete various molecules that provide protection and support of the body. For example, bone cells are surrounded by a mineralized material , making bone a hard tissue
that protects the brain and other organs and that supports the weight of the body.
- Movement.
All the movements of the body occur because of molecules located within specific cells such as muscle cells
- Communication.
Cells produce and receive chemical and electrical signals that allow them to communicate with one another. For example, nerve cells communicate with one another and with muscle
cells, causing them to contract
- Cell metabolism and energy release.
The chemical reactions that occur within cells are referred to collectively as cell metabolism. Energy released during metabolism is used for cell activities, such as the synthesis of new molecules,muscle contraction, and heat production, which helps maintain body temperature.
- Inheritance.
Each cell contains a copy of the genetic information of the individual. Specialized cells are responsible for transmitting that genetic information to the next generation
What is a cell?
- Smallest structural and functional unit of an organism capable of carrying out life processes under suitable conditions
- This is the basic unit of structure and function in a living organism
What does the cell theory state?
“A cell is the fundamental and functional unit of life”
i.e. the cell is the basic unit of the structure and function in living organisms.
What factors limit cell size?
- Surface area to volume ratio
Small cells have large surface area: Volume ratio (SA: V ratio) while large cells have a small SA: V ratio.
A large SA: V ratio enables fast rate of diffusion while a small SA: V ratio slows the rate of diffusion.
Small cells have low metabolic demands and form low amount of wastes while large cells have higher metabolic demands and form much amount of wastes.
Therefore, the large SA: V ratio in small cells enables adequate supply of oxygen and nutrients and expulsion of wastes e.g. carbon dioxide via the surface of the cell by simple diffusion while the small SA: V ratio in large cells limits diffusion hence the supply of nutrients by simple diffusion is inadequate to meet the metabolic demands of the cell.
- Nucleocytoplasmic ratio
DNA in the nucleus provides instructions for protein synthesis hence controls activities of the whole cell.
Each nucleus can only control a certain volume of cytoplasm.
Specialization forms some long / large cells, therefore to overcome this limitation such cells are modified to become multinucleate / coenocyte e.g. skeletal muscle cells and fungal hyphae.
- Fragility of cell membrane
As cell size increases, the risk of damage to the cell membrane also increases. This limits the maximum size of cells, especially animal cells.
Hence;
(i) In animals, some large sized cells take in substances in bulk by endocytosis and expel bulk
substances by exocytosis to supplement on simple diffusion.
(ii) Some animal cells increase their surface area by forming many tiny projections called microvilli.
(iii) Some cells divide when they reach a certain size to maintain suitable SA: V ratio.
Note: SA: V ratio particularly limits the size of bacterial cells, i.e. prokaryotic cells which are incapable of endocytosis and exocytosis.
- Mechanical structures that hold the cell together
Cells with tough cell walls e.g. plant cells are larger than cells with only the fragile cell membrane e.g. animal cells because the tough walls provide support and maintain cell shape.
Cells with complex internal cytoskeleton are larger than cells with little cytoskeleton because the cytoskeleton protects and supports the cell structure and maintains cell shape.
State the two types of cells?
The Prokaryote/ Prokaryotic cell
(Pro, before; karyon, nucleus) and the Eukaryote/ Eukaryotic cell (Eu, true; Karyon Nucleus) cell.
State characteristics of Prokaryote cells
- They have no membrane bound organelles.
- Their nuclear material lies in a free region known as a nucleoid e.g. in bacteria.
- The cell has no distinct nucleus. The nucleoplasm appears scattered in the cytoplasm or the nuclear
materials e.g. DNA. - The cell lacks a nuclear membrane/ envelope
- Each cell has got very few cell organelles (cell parts) e.g. they do lack the chloroplasts and mitochondria.
- The cell has circular strands of DNA in the cytoplasm, not contained in a nuclear membrane (no chromosomes)
- They are extremely small, ranging in size between 1-10milimetres in diameter
- Duplication of the chromosomes occurs but not on the spindle i.e. their cells are capable of multiplication
- The cell has got a unique cell wall containing a polysaccharide Examples include bacteria and cyanobacteria
Define ‘Eukaryotic cells’
These are cells with a true nucleus.
Their nuclear materials are found inside the nucleus surrounded by two membranes.
They probably evolved about 1000 million years ago, 2 million years after the prokaryotes.
What are the two main kinds of Eukaryotic cells?
- Plant cells
- Animal cells
Define a ‘light microscope’
A light microscope is a microscope that uses light as a source of radiation.
Under the microscope, cells are described as a small unit of living protoplasm and always surrounded by cell surface membrane and sometimes as in plants, surrounded by a non-living cell wall made of cellulose.
The most conspicuous structure is the nucleus which contains a deeply staining material known as chromatin.
When loose it is referred to as chromosome.
Chromosomes appear as thread like structures just before nuclear division.
The living material between the nucleus and the cell surface is known as the cytoplasm which contains a variety of organelles.
Define a ‘generalized cell’
This is a cell which shows all the typical features found in a cell.
Describe the features of an animal cell under the light microscope
- Contains protoplasm ( nucleus and cytoplasm) surrounded by a thin plasma membrane.
-Relatively large central nucleus surrounded by the cytoplasm.
-The nucleus contains coiled threads called chromatin.
-Chromatin contains DNA and proteins called histones which together condense to form chromosome during cell division.
-(DNA carries genetic material which controls cell activities and determines the organism’s characteristics.)
-The cytoplasm contains organelles suspended within.
Describe the structures of a plant cell under a light microscope
NB: A typical plant cell has additional specialised structures as well as many of those found in an animal cell.
- Protective, rigid, cellulose cell wall surrounding the cell.
-Plant cells have a nucleus and cytoplasm which are usually peripheral.
-The cytoplasm contains chlorophyll pigments which carry out photosynthesis.
-A large central vacuole filled with cell sap is present in mature plant cells.
- The vacuole is surrounded by the tonoplast
The most conspicuous/ clearly visible structure of the cell is the (dash) which contains chromatin.
Nucleus
- Chromatin is the loosely- coiled form of chromosomes.
- Chromosomes contain genetic material in the form of DNA.
- The nucleus is separated from the cytoplasm by its nuclear membrane
- The cytoplasm contains organelles.
State similarities between prokaryotic and eukaryotic cells
-Both have vacuoles
-Genetic material (DNA)
-Ribosomes
-Vesicles
-Cytoplasm
-Cell membrane
State differences between prokaryotic cells (p cells) and eukaryotic cells (*e cells)
P cells; The nuclear material is not enclosed by nuclear envelope
E cells;
The nuclear material is enclosed by nuclear envelope
P cells;
Organelles are not membrane bound
E cells;
Organelles are membrane bound
P cells;
Binary fission/ conjugation occurs
E cells;
Mitosis, meiosis or both can occur
P cells;
Have 70S ribosomes
E cells;
Have both 70S and 80S ribosomes
P cells;
Use mesosomes for respiration
E cells;
Use mitochondria for respiration
P cells;
Flagella if present, lack microtubules
E cells;
Flagella, if present, have a ‘9+2’ arrangement of microtubules
P cells;
Have circular DNA
E cells;
Have linear DNA
P cells;
Have photosynthetic lamellae
E cells;
Have chloroplasts in (plants and algae)
P cells;
Rigid cell wall containing murein (peptidoglycan)
E cells;
Cell walls of plants and algae contain cellulose, fungi contain chitin and animal cells have no cell walls
P cells;
Smaller in size
E cells;
Larger in size
What is the only organelle found in animal cells which is absent from plant cells?
The centriole
State advantages of having membrane bound organelles
- Potentially harmful reactants (enzymes) can be isolated inside an organelle so that they do not harm the rest of the cell
- The rate of any metabolic reactions inside an organelle can be controlled by regulating the rate at which the membrane allows the first reaction to occur or to enter
- The containment of enzymes for a particular metabolic pathway within the organelle means that the products of the reaction will always be in close proximity to the next enzymes within the sequence.
This increases the rate of metabolic reactions
- Many metabolic processes which involve enzymes occur in the membrane.
What is the function of flagella in prokaryotic cells?
Propulsion
What is an organelle?
An organelle can be defined as a membrane-enclosed
structure with specialised functions, suspended in the cytosol of eukaryotic cells.
State an example of prokaryotic cells
- Bacteria
State the main components of the cell membrane
- Phospolipids
- Proteins
- Cholesterol
- Carbohydrates
Where are mitochondria abundant?
- Kidney nephron
- Muscle fibres
- Neuron axons
- Tail of sperms
- Root hairs
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Cell Biology81
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Microscopy27
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General Knowledge24
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Chemicals Of Life122
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Histology152
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Practicals14
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Abbreviations5
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Classification25
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Movement In And Out Of Cells49
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Ecology126
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Inheritance And Evolution56
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Transport In Animals179
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Gaseous Exchange67
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Respiration44
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Nucleic Acids, Protein Synthesis & Cell Division47
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Coordination In Plants67
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Question Approach20
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The Endocrine System52
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Autotrophic Nutrition67
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Transport In Plants72
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The Nervous System174
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Behavior79
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Heterotrophic Nutrition134
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Reproduction In Plants79
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Reproduction In Animals138
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Movement, Locomotion And Support77
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Growth And Development0
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Excretion & Osmoregulation79
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Homeostasis46
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Evolution65
