Cell structure Revision Notes

Plant and animal cells both contain a cell membrane, nucleus, cytoplasm, ribosomes and mitochondria.

Both cell types may contain vacuoles, but their typical size and appearance differ.

• Cell membrane
• Nucleus
• Cytoplasm
• Ribosomes
• Mitochondria
• Vacuoles

A typical plant cell has a cell wall outside the cell membrane and may contain chloroplasts. It usually has one large vacuole.

A typical animal cell has no cell wall and no chloroplasts. Any vacuoles are usually smaller.

• Cell wall: present in plant cells and absent from animal cells.
• Chloroplasts: present in photosynthetic plant cells and absent from animal cells.
• Vacuole: typically large in a plant cell and smaller in an animal cell.

A comparison must mention both cell types in the same marking point. Use paired language such as 'whereas', 'while' or 'but'.

• Strong: Plant cells have a cell wall, whereas animal cells do not.
• Weak: Plant cells have a cell wall. This does not explicitly compare both cells.
• Only compare structures named or shown in the question.

The cell wall surrounds the bacterial cell, providing shape and protection against damage and bursting.

Inside the cell wall is the cell membrane, which controls the movement of substances in and out of the cell.

The cytoplasm is a jelly-like substance where chemical reactions occur and where ribosomes are found.

Ribosomes are small structures that synthesize proteins needed by the cell.

Bacteria have circular DNA that contains the genetic information necessary for cell functions.

Plasmids are small, circular DNA molecules separate from the main chromosome, often carrying extra genes such as antibiotic resistance.

• Cell wall: shape and protection.
• Cell membrane: controls substance movement.
• Cytoplasm: site of chemical reactions and ribosomes.
• Ribosomes: protein synthesis.
• Circular DNA: main genetic material.
• Plasmids: extra genetic information.

Bacteria lack a nucleus; their DNA is free in the cytoplasm as a circular chromosome.

Plasmids can be transferred between bacteria, aiding adaptation and survival.

Bacterial cells are prokaryotic, simpler than eukaryotic plant and animal cells.

• No nucleus present.
• DNA is circular and free in cytoplasm.
• Plasmids carry beneficial genes and can be shared.

Unlike plant and animal cells, bacteria do not have membrane-bound organelles such as mitochondria or a nucleus.

Their simpler structure allows rapid reproduction and adaptation.

Understanding bacterial cell structure is important for microbiology and medicine.

• No membrane-bound organelles.
• Simpler, smaller cells.
• Important in health and disease contexts.

Plant cells have a rigid cell wall, chloroplasts for photosynthesis, and a large permanent vacuole for storage and support.

They also contain a cell membrane, cytoplasm, and a nucleus controlling cell activities.

• Cell wall present.
• Chloroplasts present.
• Large permanent vacuole present.
• Nucleus and cell membrane present.

Animal cells have a flexible cell membrane, cytoplasm, and a nucleus.

They lack a cell wall, chloroplasts, and large permanent vacuoles found in plant cells.

• No cell wall.
• No chloroplasts.
• No large permanent vacuole.
• Nucleus and cell membrane present.

Bacterial cells have a cell wall and cell membrane but no nucleus or chloroplasts.

They contain cytoplasm, plasmids (small DNA rings), and a single circular DNA strand.

Recognizing these features helps distinguish bacteria from plant and animal cells.

• Cell wall and membrane present.
• No nucleus or chloroplasts.
• Plasmids and circular DNA present.

The cell wall provides support and protection, maintaining cell shape and preventing bursting.

Chloroplasts carry out photosynthesis, converting light energy into chemical energy (food).

The large permanent vacuole stores water and nutrients and helps maintain cell rigidity by exerting turgor pressure.

The nucleus controls cell activities by regulating gene expression.

Mitochondria produce energy through aerobic respiration.

The cell membrane controls movement of substances in and out of the cell.

• Cell wall: support and protection.
• Chloroplasts: photosynthesis.
• Vacuole: storage and rigidity.
• Nucleus: controls activities.
• Mitochondria: energy production.
• Cell membrane: regulates substance movement.

Animal cells have a flexible cell membrane controlling substance movement.

The nucleus regulates cell functions and contains genetic material.

Mitochondria generate energy through respiration to power cellular activities.

Animal cells may have small vacuoles for storage but lack a cell wall and chloroplasts.

• Cell membrane: controls substance movement.
• Nucleus: controls activities.
• Mitochondria: produce energy.
• Small vacuoles may be present.

The cell wall provides shape and protection against damage and osmotic pressure.

The cell membrane regulates entry and exit of substances.

Cytoplasm is the site of chemical reactions and contains ribosomes for protein synthesis.

Bacterial DNA is circular and free in the cytoplasm, controlling cell functions.

Plasmids carry extra genes that can provide advantages like antibiotic resistance.

Bacteria lack mitochondria and perform energy production in the cytoplasm and membrane.

• Cell wall: shape and protection.
• Cell membrane: controls substance movement.
• Cytoplasm: site of reactions and ribosomes.
• Circular DNA: genetic control.
• Plasmids: extra genes.
• No mitochondria present.

All living cells originate from the division of pre-existing cells. This means that cells cannot appear out of nowhere; instead, an existing cell divides to produce two new cells. This fundamental process supports the growth of organisms, the repair of damaged tissues, and the replacement of old cells.

• New cells arise only when existing cells divide.
• Cell division is essential for growth and healing.
• Spontaneous formation of cells does not occur.

Cell division allows organisms to increase their number of cells during growth. It also replaces cells that are worn out or damaged, maintaining the organism's health. Without cell division, organisms would not be able to develop or recover from injury.

• Supports organism growth by increasing cell numbers.
• Enables repair by replacing damaged cells.
• Maintains tissue and organ function through cell renewal.

Some may think cells can form spontaneously, but this is incorrect. Understanding that all cells come from existing cells helps explain biological continuity and inheritance.

• Cells do not form spontaneously.
• All cells have a parent cell.
• Cell division ensures genetic continuity.

- Ciliated cells have tiny hair-like structures called cilia that move mucus along the trachea and bronchi, helping to clear dust and microbes.

- Root hair cells have long extensions to increase surface area for absorbing water and minerals from the soil.

- Palisade mesophyll cells contain many chloroplasts to efficiently carry out photosynthesis.

- Neurones conduct electrical impulses rapidly throughout the body.

- Red blood cells transport oxygen by containing haemoglobin and having a biconcave shape to maximize surface area.

- Gametes (sperm and egg cells) are specialized for reproduction; sperm cells are motile to reach the egg, and egg cells provide nutrients for the developing embryo.

• Ciliated cells move mucus in airways.
• Root hair cells absorb water and minerals.
• Palisade mesophyll cells perform photosynthesis.
• Neurones transmit electrical signals.
• Red blood cells carry oxygen.
• Gametes enable reproduction.

Each specialized cell has features that help it perform its role effectively. For example, cilia on ciliated cells beat rhythmically to move mucus. Root hair cells have long extensions to increase absorption area. Palisade cells have many chloroplasts to capture sunlight. Neurones have long fibers to transmit impulses quickly. Red blood cells lack a nucleus to maximize space for haemoglobin. Sperm cells have tails for movement, while egg cells are large to store nutrients.

• Cilia enable mucus movement.
• Extensions increase absorption surface area.
• Chloroplasts capture light energy.
• Long fibers conduct impulses.
• Biconcave shape increases oxygen transport.
• Motility and nutrient storage aid reproduction.

Specialization allows cells to perform tasks efficiently, supporting the organism's overall function. Understanding these cells helps explain how complex processes like respiration, nutrition, and reproduction occur.

• Specialized cells perform distinct roles.
• Cell structure matches function.
• Supports organism survival and reproduction.

- Cell: The smallest unit of life capable of independent function. Example: nerve cell.

- Tissue: A group of similar cells working together to perform a specific function. Example: muscle tissue.

- Organ: A structure made of different tissues working together to perform a function. Example: heart.

- Organ system: A group of organs working together to carry out a major function. Example: circulatory system.

- Organism: A complete living individual made up of organ systems. Example: human.

• Cell: basic unit of life.
• Tissue: similar cells with common function.
• Organ: different tissues combined.
• Organ system: multiple organs working together.
• Organism: whole living being.

Cells combine to form tissues, tissues combine to form organs, organs work together in organ systems, and organ systems make up an organism. This hierarchical structure allows complex functions to be carried out efficiently.

• Cells → tissues → organs → organ systems → organism.
• Each level is more complex than the previous.
• Coordination at all levels is essential for life.

Knowing these definitions helps in studying biology by clarifying how living things are organized and how different parts contribute to overall function.

• Clarifies biological structure and function.
• Supports learning about body systems.
• Helps in understanding health and disease.