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24 Feb 2026

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51 pages

Comprehensive LC Biology Notes and Diagrams

Chloe Ahern

@chloeahern

Ever wondered what's actually inside the cells that make up... Show more

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# CHAPTER 7

# cell structure

Ultrastructure The detail of a structure as seen through an electron microscope

Animal Cell

Plant Cell

nuc

Cell Structure Basics

Your body is made up of trillions of cells, and understanding their ultrastructure (what you see under powerful microscopes) is key to biology success. Think of cells as tiny factories with different departments doing specific jobs.

Animal cells and plant cells share many features but have crucial differences. Both have a nucleus (the control centre), cytoplasm $the jelly-like filling$ , and ribosomes (protein makers). The cell membrane acts like a selective bouncer, controlling what gets in and out using its phospholipid bilayer structure.

Mitochondria are your cell's power stations, producing energy through aerobic respiration. They're packed with folded membranes to maximise surface area - you'll find loads of them in active cells like neurons that need tons of energy.

Quick Tip: Remember that mitochondria have their own DNA and reproduce independently - they're like tiny organisms living inside your cells!

Plant vs Animal Cells

Plant cells have some extra features that animal cells don't. The cell wall made of cellulose gives plants their rigid structure and shape - imagine it as a protective outer shell around the cell membrane.

Chloroplasts are the green powerhouses where photosynthesis happens. These double-membraned organelles contain chlorophyll and have stacked membranes called grana that capture sunlight. Plant cells also have a large central vacuole filled with sap that helps maintain the plant's shape and stores materials.

The nucleus is the brain of any cell, containing chromosomes (which become chromatin when not dividing). Nuclear pores let important molecules like mRNA pass through. Cytoplasm is 90% water and houses all the organelles where metabolic reactions occur.

Remember: All the living parts of a cell together are called protoplasm - this includes everything except the cell wall!

Prokaryotic vs Eukaryotic Cells

Understanding the difference between eukaryotic and prokaryotic cells is crucial for your exams. Eukaryotic cells (like yours) have a membrane-bound nucleus and organelles - they're the advanced, complex cells found in animals, plants, and fungi.

Prokaryotic cells are much simpler - think bacteria. They have no membrane-bound nucleus, just DNA floating in a circular loop. No fancy organelles either, and they're much smaller than eukaryotic cells.

Light microscopes can magnify up to 1,500 times and show basic cell structures. Electron microscopes are the real game-changers, magnifying up to 1,000,000 times and revealing incredible detail. Understanding how to use a light microscope properly is essential lab skill.

Lab Success: Always start with low power objective lens, use coarse focus first, then switch to high power and use fine focus for crisp images!

Microscope Experiments

Preparing cell samples is a key practical skill you'll need to master. For plant cells, onion epidermis works brilliantly - it's thin, easy to handle, and shows cell walls clearly when stained with iodine solution.

Animal cells from your cheek are perfect for observation. A gentle rub with a cotton bud gives you plenty of cells to examine. Methylene blue stain makes the nucleus and cell membrane visible under the microscope.

The technique is crucial: place your sample on a slide with a drop of water, add stain, then lower the coverslip at an angle to avoid air bubbles. Always blot excess liquid to prevent mess and improve image quality.

Pro Tip: When switching from low to high power, always centre your specimen first - high power has a much smaller field of view!

Cell Division Introduction

Cell continuity means all cells come from pre-existing cells - they don't just appear from nowhere. Understanding chromosomes (coiled DNA and protein threads) is essential since they carry genes that control protein production.

Diploid cells (like most of your body cells) have two sets of chromosomes $2n = 46 in humans$ . Haploid cells (sperm and egg) have just one set $n = 23$ . When fertilisation happens, you get back to the full diploid number.

The cell cycle describes everything that happens between one cell division and the next. Most of this time is spent in interphase, when the cell grows, makes new organelles, and crucially, replicates its DNA ready for division.

Key Concept: Homologous pairs are matching chromosomes with the same genes - you get one from each parent!

Mitosis Process

Interphase takes up 90% of the cell cycle. During this time, chromatin is elongated and thin, the cell grows, and DNA replication occurs. After replication, each chromosome consists of two identical sister chromatids joined at the centromere.

Mitosis has four clear stages you need to know. Prophase sees chromosomes becoming visible and the nuclear membrane breaking down. Metaphase is when chromosomes line up at the cell's equator, attached to spindle fibres.

Anaphase is dramatic - centromeres split and sister chromatids are pulled to opposite poles by contracting spindle fibres. Telophase reverses the early changes: new nuclear membranes form and chromosomes elongate back to chromatin.

Memory Trick: Remember PMAT - Prophase, Metaphase, Anaphase, Telophase - for the order of mitotic stages!

Cell Division Functions

Cytokinesis (actual cell splitting) happens differently in plants and animals. Animal cells form a cleavage furrow that pinches the cell in two. Plant cells can't pinch due to their rigid cell walls, so they build a new cell plate from the centre outwards.

Mitosis serves different purposes depending on the organism. In single-celled organisms like bacteria, it's their method of reproduction. In multicellular organisms like you, it's essential for growth and repair of damaged tissues.

The process ensures each new cell gets an identical copy of genetic information. This is crucial for maintaining consistent cell function throughout your body.

Real-world Application: Every time you heal from a cut, mitosis is working to replace damaged skin cells with identical healthy ones!

Meiosis and Cancer

Meiosis produces gametes (sex cells) with half the chromosome number of parent cells. Unlike mitosis, meiosis creates genetic variation through gene combination, which is essential for evolution and species survival.

Sexual reproduction maintains species chromosome numbers across generations. When sperm $n=23$ meets egg $n=23$ , fertilisation produces a zygote with the full diploid number $2n=46$ .

Cancer occurs when cells lose control over mitosis rates. Benign tumours eventually stop dividing and don't spread. Malignant tumours divide uncontrollably, invade other tissues, and can spread through the bloodstream (metastasis). Carcinogens like UV radiation and cigarette smoke damage genes that normally control cell division.

Health Connection: Understanding how normal cell division works helps explain why cancer treatments often target rapidly dividing cells!

Cell Organisation

Tissues are groups of similar cells working together for the same function. Plants have four main tissue types: meristematic (growth), dermal (protection), ground (photosynthesis and storage), and vascular (transport).

Dermal tissue like epidermis protects plants with a waxy cuticle layer. Vascular tissue includes xylem (transports water and minerals upwards) and phloem (transports food from leaves to other parts).

Animal tissues include epithelial (covering surfaces), connective (support and joining), muscular (movement), and nervous (communication). Nervous tissue contains neurons that carry electrical signals around your body.

Study Strategy: Learn tissue types by their functions first, then worry about detailed structures - function determines form!

Tissue Culture and Organs

Tissue culture grows cells outside the organism in sterile conditions. Micropropagation in plants can produce thousands of identical plants from just a few cells, perfect for agriculture and conservation.

Medical applications include growing skin for grafts using stem cells from embryos, bone marrow, or umbilical cords. This avoids rejection issues and eliminates the need to damage healthy skin for traditional grafts.

Organs combine multiple tissues to perform complex functions. A leaf combines dermal tissue (epidermis), vascular tissue (transport), and ground tissue (photosynthesis). Your heart combines muscular tissue (pumping), epithelial tissue (lining), nervous tissue (pacemaker control), and connective tissue (support).

Future Focus: Tissue culture technology is revolutionising medicine and agriculture - understanding these basics opens doors to exciting career possibilities!

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Biology

•

24 Feb 2026

•

51 pages

Comprehensive LC Biology Notes and Diagrams

Chloe Ahern

@chloeahern

The process ensures each new cell gets an identical copy of genetic information. This is crucial for maintaining consistent cell function throughout your body.

Real-world Application: Every time you heal from a cut, mitosis is working to replace damaged skin cells with identical healthy ones!

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Meiosis and Cancer

Sexual reproduction maintains species chromosome numbers across generations. When sperm $n=23$ meets egg $n=23$ , fertilisation produces a zygote with the full diploid number $2n=46$ .

Health Connection: Understanding how normal cell division works helps explain why cancer treatments often target rapidly dividing cells!

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Access to all documents

Improve your grades

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Cell Organisation

Study Strategy: Learn tissue types by their functions first, then worry about detailed structures - function determines form!

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Access to all documents

Improve your grades

Join milions of students

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Tissue Culture and Organs

Future Focus: Tissue culture technology is revolutionising medicine and agriculture - understanding these basics opens doors to exciting career possibilities!