GCE Biology
Past Questions

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**The reasoning** Cell walls are **rigid, protective structures** found outside the cell membrane. Plants need them for: - **Structural support** — to stand upright without a skeleton - **Protection** — against pathogens and physical stress - **Shape maintenance** — plant cells stay firm and boxed The cell wall is made of **cellulose** (a tough carbohydrate). Animals don't have this because we have skeletons for support and need our cells to be **flexible** for movement — imagine if your muscle cells were boxed in rigid walls! **Why the wrong options tempt you** - **A (Animal)** — You might confuse cell wall with cell *membrane*, which both plants AND animals have. But the membrane is thin and flexible; the wall is thick and rigid. - **C (Both)** — Tricky! Both have membranes, but only plants have walls. - **D (Neither)** — This contradicts basic biology — plants definitely have cell walls. **Quick takeaway** **Plants = Cell Wall + Membrane** (for strength and structure); **Animals = Membrane only** (for flexibility). Think: "Plants stand, animals move — cell walls vs. no walls."

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**The reasoning** The human heart is a double pump divided into **four chambers**: two upper chambers called **atria** (singular: atrium) and two lower chambers called **ventricles**. Think of it like a duplex with an upstairs and downstairs on both sides. - **Right atrium** receives deoxygenated blood from the body - **Right ventricle** pumps it to the lungs for oxygen - **Left atrium** receives oxygenated blood from the lungs - **Left ventricle** pumps it out to the entire body This four-chamber system separates oxygen-poor and oxygen-rich blood completely, making our circulation highly efficient. **Why the wrong options tempt you** **2 chambers** — You might think "left and right" and stop there, forgetting each side has two parts. **3 chambers** — Some animals like amphibians (frogs) actually have three chambers, so this confuses students who mix up different species. **5 chambers** — Just a distractor; no vertebrate has five heart chambers. **Quick takeaway** Remember: **"Two up, two down" — humans have 4 heart chambers** (2 atria receiving, 2 ventricles pumping), which keeps our blood circulation separate and efficient.

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## The reasoning The atmosphere around us is a **mixture of gases**, not pure oxygen. By volume, air contains approximately: - **78% Nitrogen** (the most abundant) - **21% Oxygen** (what we need for respiration) - **1% other gases** (argon, carbon dioxide, trace gases) So the air you're breathing right now is roughly **one-fifth oxygen**. This 21% is perfectly balanced for life — enough to keep us alive, but not so much that everything catches fire easily! ## Why the wrong options tempt you **10%** — Too low! This might come from confusing oxygen with carbon dioxide (which is only about 0.04%). **50%** — This feels intuitive because "we need oxygen to survive," but half the air being oxygen would make combustion way too easy and dangerous. **75%** — This probably confuses oxygen with nitrogen, which actually makes up about 78% of air. ## Quick takeaway **Remember the "78-21-1 rule"**: Air is roughly 78% nitrogen, 21% oxygen, and 1% everything else — we breathe a nitrogen-rich mix, not pure oxygen!

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**The reasoning** Insulin is a hormone that controls blood sugar (glucose) levels in your body. It's produced by special cells called **beta cells** located in clusters called the **islets of Langerhans** within the **pancreas**. Think of it this way: When you eat rice or garri, your blood sugar rises. The pancreas detects this and releases insulin, which acts like a "key" that unlocks your cells so glucose can enter and give you energy. Without insulin, sugar stays in your blood — that's what happens in diabetes. **Why the wrong options tempt you** - **A) Liver** — The liver *stores* glucose as glycogen and can break it down when needed, but it doesn't *make* insulin. Easy to confuse because both organs deal with blood sugar regulation. - **C) Heart & D) Lungs** — These pump blood and exchange oxygen, respectively. They have nothing to do with hormone production for sugar control. **Quick takeaway** **Pancreas = Insulin factory.** Remember: "**Pan**-creas **Ins**ulin" — both start with similar sounds, and the pancreas sits behind your stomach managing your sugar levels!

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**The reasoning** Plants have a vascular system—think of it like roads for transportation. There are two main "highways": **xylem** and **phloem**. **Phloem** is responsible for transporting *food* (sugars made during photosynthesis) from the leaves (where food is produced) to all other parts of the plant—roots, stems, fruits, flowers. This movement of food is called **translocation**, and it flows in multiple directions (up and down) as needed. **Why the wrong options tempt you** - **Xylem (A)** transports *water and minerals* from roots upward—not food. Many students confuse the two vessels because they work together. - **Cortex (C)** is just storage tissue in stems and roots; it doesn't transport anything. - **Bark (D)** is the outer protective layer; while it *contains* phloem inside it, bark itself isn't the transport tissue. **Quick takeaway** **"Phloem = Food"**—both start with "F." Xylem carries water UP from roots; phloem carries food FROM leaves to everywhere the plant needs energy. Remember: phloem is the plant's food delivery service! 🌱

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**The reasoning** The adult human skeleton contains **approximately 206 bones**. This is a fundamental anatomy fact you need to memorize for your exams. Here's the key: babies are actually born with about 270 bones, but as we grow, many bones **fuse together**. For example, the skull bones merge, and bones in the spine join up. By the time you're an adult (around 20-25 years old), you're left with roughly 206 bones. The breakdown: skull (~22), spine (~26), ribs and sternum (~25), arms (~60), legs (~60), plus smaller bones in hands and feet. **Why the wrong options tempt you** - **100** is too low — that's barely half! Students might confuse this with major bone groups. - **150** sounds "reasonable" if you're just guessing somewhere in the middle. - **300** catches people who remember babies have more bones but forget about the fusion process as we mature. **Quick takeaway** Remember: **"Born with 270, grow to 206"** — bones fuse as you mature, leaving adults with approximately 206 bones.

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**The reasoning** DNA (Deoxyribonucleic Acid) is the genetic material that contains all your hereditary information — the "instruction manual" for building and running your body. In eukaryotic cells (like human, animal, and plant cells), DNA is stored in the **nucleus**, which acts like a protected vault or library. The nucleus has a double membrane that keeps DNA safe and organized. Think of it as the "control center" of the cell where genetic instructions are kept and copied when needed. **Why the wrong options tempt you** - **B) Membrane** — The cell membrane is just the outer boundary; it controls what enters/exits but doesn't store DNA. - **C) Cell wall** — Only plants, fungi, and bacteria have cell walls. It's a rigid outer support structure, not a storage place for genetic material. - **D) Vacuole** — This stores water, nutrients, and waste in plant cells, not DNA. **Quick takeaway** Remember: **Nucleus = News center** — it houses the DNA "news" that controls everything happening in your cell.

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All living things are made of cells — the smallest functional unit.

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Mitochondria produce ATP (cellular energy) through aerobic respiration.

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Photosynthesis converts CO₂ and water into glucose using sunlight energy.

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Haemoglobin in red blood cells binds oxygen and transports it from lungs to tissues.

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DNA = Deoxyribonucleic Acid — carries genetic information in cells.

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The skin is the largest organ — about 2 square metres in adults.

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Insects exchange gases via spiracles (openings) leading to tracheal tubes throughout the body.

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O-negative red cells have neither A, B, nor Rh antigens, so they can be given to any recipient.