Unit 2 IGCSE Biology Explained for Students

Welcome to our exploration of cell structure and organization!Cells are the basic units of life, and come in two main types: animal cells and plant cells.Let's first look at an animal cell. Notice its flexible membrane and multiple small vacuoles.Now, observe a plant cell. It has additional structures like a rigid cell wall and chloroplasts.Let's compare the key differences between plant and animal cells.This table highlights the main structural differences between plant and animal cells.Now, let's examine the specific functions of each major organelle.To understand the scale of cells, let's compare their sizes to familiar objects.Now that we understand the basic structure of cells, we're ready to explore how substances move in and out of them.Cellular transport occurs through three main mechanisms: diffusion, osmosis, and active transport.Diffusion is the movement of molecules from areas of high concentration to low concentration.Osmosis is the movement of water molecules across a selectively permeable membrane.Active transport requires energy in the form of ATP to move molecules against their concentration gradient.We can observe diffusion in everyday life, such as when a tea bag is placed in hot water.In a classic osmosis experiment, a potato strip placed in salt solution loses water through osmosis.Enzymes are specialized proteins that act as biological catalysts. They work through a lock-and-key mechanism.The substrate fits perfectly into the enzyme's active site, like a key into a lock.Enzyme activity is highly dependent on pH. Most enzymes work best at neutral pH, around 7.Temperature also affects enzyme activity. The optimal temperature for human enzymes is around 37 degrees Celsius, or body temperature.Different types of enzymes break down specific nutrients. Amylase breaks down carbohydrates.Protease enzymes break down proteins into amino acids.And lipase breaks down lipids into fatty acids and glycerol.Each enzyme is specific to its substrate. When they work, they break large molecules into smaller ones.Enzyme activity can be blocked by inhibitors, which prevent the substrate from binding.When an inhibitor binds to the enzyme's active site, the substrate can no longer attach.After catalyzing a reaction, enzymes are not consumed and can be used again.Inside plant cells, specialized organelles called chloroplasts contain the machinery for photosynthesis.Chlorophyll molecules in the thylakoids absorb light energy to power photosynthesis.In the light-dependent reactions, electrons flow through protein complexes in the thylakoid membrane.The Calvin cycle uses the energy from light reactions to produce glucose from carbon dioxide.The rate of photosynthesis is affected by temperature, light intensity, and carbon dioxide concentration.We can observe photosynthesis in action by watching oxygen bubbles produced by water plants.The digestive system breaks down food through mechanical and chemical digestion.Different enzymes help break down specific nutrients in our food.The heart pumps blood through four chambers, coordinating the flow of oxygen-rich and oxygen-poor blood.Blood vessels form a complex network for transporting nutrients and oxygen.Different nutrients are transported through the bloodstream to reach cells throughout the body.Let's review the key points about animal nutrition and transport.Congratulations on completing this comprehensive journey through biology!