CAIE Biology IGCSE - 2 - Organisation of the Organism - Notes

Sep 5, 2026

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Structured biology study notes for CAIE Biology IGCSE topic 2, focusing on how organisms are organised from cells to larger levels. Covers the main parts of animal and plant cells, key similarities and differences, and the functions of cytoplasm, cell membrane, nucleus, ribosomes, and mitochondria. Extends to plant-only features like vacuoles, chloroplasts, and cell walls, plus bacterial and specialised cells, then introduces tissue, organ, and organ system definitions and specimen sizing calculations using microscopy and magnification.

LanguageEnglish

CategoryExam

FormatPDF

Pages8

Reading Time20 min

AccessFree to download

Cell Structure

Comparing the structure of animal cells and plant cells

Functions of cell structures in animal and plant cells

In plants only

Bacterial cells

Specialised cells

Levels of organisation

Size of specimens

CAIE Biology IGCSE 2:Organisation of the OrganismNotes (Content in bold is for Extended students only) # Cell Structure ## Comparing the structure of animal cells and plant cells: Similarities: ● They both contain a nucleus,cytoplasm,mitochondria,ribosomes and a cellmembrane. ## Differences: ● Plant cells contain a cell wall,vacuole and chloroplasts. ● Plant cells have a more regular shape and are larger. ## Animal cells Plant cells ribosomes www.pmt.education PMTEducation ## Functions of cell structures in animal and plant cells: ● Cytoplasm-A jelly-like material within the cell in which reactions occur.The cytoplasmcontains structures such as ribosomes and vesicles. ● Cell membrane-a thin membrane that surrounds the cell,controls entry and exit ofsubstances. ● Nucleus -the nucleus contains genetic material in the form of DNA which codes forproteins.DNA replication also occurs in the nucleus. ● Ribosomes-Ribosomes are the site of protein synthesis. ● Mitochondria -site of respiration.Provides energy for the cell to function. ## In plants only: ● Vacuole-is a fluid-filled sac containing mineral salts,sugars,amino acids,wastesubstances and pigments which colour the cell and attract pollinating insects. ·Chloroplasts -the site of photosynthesis,which allows plants to convert light energy toglucose. ● Cellwall-gives the cell structure and prevents bursting.It is made of cellulose. ## Bacterial cells: ● Bacterial cells contain a cell wall,cell membrane,cytoplasm and ribosomes. ● The cell wall of a bacterial cell is made of a different material than in plant cells.Thismaterial is called peptidoglycan. ● Bacterial cells do not have a nucleus but instead contain circular DNA-a loop of DNAwhich floats in the cytoplasm. ● The circular DNA contains most of the genetic material in the cell. ● These cells also lack mitochondria and chloroplasts. ● Bacterial cells contain plasmids.Plasmids are small rings of DNA. cell wall Loop of DNA ribosomes New cells are produced by the division of existing cells. ## Specialised cells: Cells and tissues are specialised to carry out their particular function.Examples of specialisedcells are: ● Ciliated cells -ciliated cells are found lining the trachea.They have hair-like projectionscalled cilia which move together to transport mucus,dust and bacteria upwards to thethroat. nucleus ● Root hair cells -are adapted to have a large surface area.This speeds up the rate ofosmosis and mineral ion uptake in plants. CytoplasmVacuole NucleusCell wall ● Palisade mesophyll cells -this is where photosynthesis occurs.Mesophyll cells are talland closely packed to efficiently absorb light and contain lots of chloroplasts forphotosynthesis.They are also placed at the top of the leaf where most of the light hits,enabling them to absorb as much light energy as possible. ● Neurones-nerve cells are adapted to rapidly transmit electrical impulses.Nerve cellsare myelinated,which insulates the cell and prevents the impulse weakening andslowing down.They also contain lots of mitochondria to provide energy.Dendrites havea large surface area and are branched to receive impulses from many other neurons. ● Red blood cells -red blood cells contain haemoglobin which allows them to carryoxygen around the body.They have a biconcave shape which increases their surfacearea,allowing for rapid diffusion.They also have thin cell membranes to decrease thediffusion distance.They do not contain a nucleus,thus have more space for oxygen. ● Sperm cells -sperm cells are gametes.Gametes are the reproductive cells of organismswith half the chromosomes of normal cells.Sperm cells are adapted by containing lotsof mitochondria so that the cell has enough energy to reach the egg cell.It has a tail toallow movement and contains digestive enzymes to help penetrate the egg cellmembrane. Tail ● Egg cells -egg cells are also gametes.Egg cells have nutrients in their cytop

FAQs

What are the key similarities and differences between animal and plant cells?

Animal and plant cells both contain a nucleus, cytoplasm, mitochondria, ribosomes, and a cell membrane. Plant cells also have a cell wall, vacuole, and chloroplasts, and they are usually larger with a more regular shape.

What do cell structures do in animal and plant cells?

Cytoplasm is where reactions occur. The cell membrane controls entry and exit of substances. The nucleus contains DNA and supports DNA replication; ribosomes are for protein synthesis; mitochondria provide energy through respiration.

How do you calculate the actual size of a specimen under a microscope?

Use Actual size = Image size / Magnification. If answers are required in micrometres, convert by multiplying millimetres by 1000 (1 mm = 1000 μm).

Sep 5, 2026

Upload by Aditya