Science2 views·Updated Jun 3, 2026·7 pages

Understanding Cells: Structures and Functions

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Every living thing on Earth is made up of cells...

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The Cell: Basic Unit of Life

You're constantly surrounded by trillions of cells - they're literally everywhere, including the roughly 37 trillion that make up your own body! Cells are the fundamental building blocks of all living organisms, and every single life process happens at the cellular level.

There are two main types of cells you need to know. Prokaryotic cells are the simple ones - think bacteria - that don't have a proper nucleus or organised compartments. Eukaryotic cells are the complex ones that make up plants, animals, and fungi, complete with a nucleus and specialised compartments called organelles.

Living things can be unicellular (made of just one cell, like bacteria) or multicellular (made of many cells working together, like you). For your Leaving Cert, you'll mainly focus on eukaryotic cells, particularly plant and animal cells.

Remember: Organelles are like the "organs" of a cell - each one has a specific job to keep the cell functioning properly.

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Animal Cell Structure

Animal cells are your basic cellular template - they're usually round or irregular in shape and packed with amazing tiny machines. The cell membrane acts like a bouncer at a club, deciding what gets in and out of the cell using its selective permeability.

Inside, the cytoplasm is like a jelly-filled workspace where loads of chemical reactions happen. The nucleus is absolutely crucial - it's the control centre containing all your genetic material (DNA) wrapped up in chromosomes, surrounded by its own protective membrane.

Mitochondria are the real heroes here - they're often called the "powerhouses" because they carry out respiration to release energy as ATP. Muscle cells are packed with these because they need loads of energy! Ribosomes are tiny protein-making factories that can float freely or attach to the endoplasmic reticulum.

Top Tip: Cells that need more energy (like heart muscle cells) contain way more mitochondria - this shows how structure relates to function!

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More Animal Cell Components

The endoplasmic reticulum (ER) is like the cell's internal highway system for transporting materials. There are two types: rough ER (covered in ribosomes, looks bumpy) handles proteins, whilst smooth ER (no ribosomes) deals with lipids and other substances.

Vesicles are like tiny delivery vans - small membrane-bound sacs that transport substances around the cell. They're constantly moving materials from one place to another, keeping everything organised.

These organelles work together like a well-oiled machine. When you understand how each part contributes to the whole system, cell biology starts making perfect sense!

Exam Smart: Remember that animal cells can have small, temporary vacuoles, but they're nothing like the massive ones in plant cells.

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Plant Cell Structure

Plant cells are like upgraded animal cells with some brilliant extras that help them make their own food and stand upright. They typically have a more fixed, rectangular shape thanks to their rigid cell wall made of cellulose.

The cell wall is the plant's suit of armour - it provides structural support and protection whilst being fully permeable (unlike the selective cell membrane). This is why plants can grow so tall without collapsing!

Chloroplasts are the green magic-makers containing chlorophyll, the pigment that captures sunlight for photosynthesis. You'll find loads of these in leaf cells because that's where most photosynthesis happens. They're basically the plant's solar panels!

Key Point: Plant cells have all the same organelles as animal cells PLUS the cell wall, chloroplasts, and a large central vacuole.

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Plant Cell Specialities and Comparison

The large central vacuole is like a plant cell's storage tank and support system rolled into one. It's filled with cell sap (water, salts, and sugars) and helps maintain the cell's shape by pushing outwards against the cell wall - this is called turgor pressure.

Here's a handy comparison: animal cells are irregular and flexible, whilst plant cells are fixed and rectangular. Animal cells store energy as glycogen, plants use starch. Most importantly, plants can photosynthesise thanks to their chloroplasts, whilst animals must get their energy by eating other organisms.

When tackling exam questions, think about structure matching function. Leaf cells packed with chloroplasts? Perfect for photosynthesis. Sperm cells loaded with mitochondria? Ideal for that energy-demanding swim to reach an egg!

Exam Tip: Don't confuse the cell wall (structural support, fully permeable) with the cell membrane $selective control of entry/exit$ - plants have both!

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Prokaryotic vs Eukaryotic Cells

Understanding the difference between prokaryotic and eukaryotic cells is absolutely essential for your exams. Prokaryotic cells (like bacteria) are the minimalists of the cell world - no nucleus, no membrane-bound organelles, just DNA floating freely in a region called the nucleoid.

Eukaryotic cells are the complete opposite - they've got a proper nucleus with DNA neatly packaged inside, plus loads of specialised organelles doing different jobs. They're also much larger than prokaryotic cells $think 10-100 μm versus just 1-5 μm$ .

Remember the word origins: "pro" means before, "eu" means true, and "karyon" means nucleus. So prokaryotic = "before nucleus" (evolved first, no proper nucleus) and eukaryotic = "true nucleus" (evolved later, has a proper nucleus).

Memory Trick: Think of prokaryotic cells as studio apartments (everything in one space) and eukaryotic cells as mansions (lots of separate rooms with specific purposes).

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Key Takeaways for Success

Here's what you absolutely must remember: all living things are made of cells, and there are two main types - prokaryotic (bacteria) and eukaryotic (plants, animals, fungi). Animal cells have the basic kit: cell membrane, cytoplasm, nucleus, mitochondria, and ribosomes.

Plant cells have everything animal cells have, plus three crucial extras: a cell wall for support, chloroplasts for photosynthesis, and a large central vacuole for storage and structure. Each organelle has a specific job that matches its structure perfectly.

Common exam mistakes to avoid: don't mix up cell walls and cell membranes, remember that plants DO respire (they need energy too!), and always be specific about functions rather than using vague terms like "the nucleus is the brain."

Final Tip: When answering exam questions, always explain WHY a cell has certain organelles by linking structure to function - this shows real understanding!

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Science2 views·Updated Jun 3, 2026·7 pages

Understanding Cells: Structures and Functions

Add to Google sources

Every living thing on Earth is made up of cells - from the tiniest bacteria to massive whales and towering oak trees. Think of cells as the LEGO blocks of life: they're the smallest units that can actually be called...

of 7

The Cell: Basic Unit of Life

Remember: Organelles are like the "organs" of a cell - each one has a specific job to keep the cell functioning properly.

of 7

Animal Cell Structure

Top Tip: Cells that need more energy (like heart muscle cells) contain way more mitochondria - this shows how structure relates to function!

of 7

More Animal Cell Components

These organelles work together like a well-oiled machine. When you understand how each part contributes to the whole system, cell biology starts making perfect sense!

Exam Smart: Remember that animal cells can have small, temporary vacuoles, but they're nothing like the massive ones in plant cells.

of 7

Plant Cell Structure

Key Point: Plant cells have all the same organelles as animal cells PLUS the cell wall, chloroplasts, and a large central vacuole.

of 7

Plant Cell Specialities and Comparison

Exam Tip: Don't confuse the cell wall (structural support, fully permeable) with the cell membrane $selective control of entry/exit$ - plants have both!

of 7

Prokaryotic vs Eukaryotic Cells

Memory Trick: Think of prokaryotic cells as studio apartments (everything in one space) and eukaryotic cells as mansions (lots of separate rooms with specific purposes).

of 7

Key Takeaways for Success

Final Tip: When answering exam questions, always explain WHY a cell has certain organelles by linking structure to function - this shows real understanding!