Photosynthesis - How Plants Make Their Own Food

Ever wondered how plants survive without popping to Tesco for a meal? They've got their own incredible food-making process called photosynthesis, and it's happening in every green leaf around you right now.

The basic equation is simple: carbon dioxide + water → glucose + oxygen (using light energy). Plants absorb CO₂ through tiny pores called stomata in their leaves, whilst water travels up from the roots through the xylem. The magic happens in chloroplasts, which contain the green pigment chlorophyll that captures light energy.

This process is endothermic - it needs energy input to work. The glucose produced becomes the plant's food source, whilst oxygen gets released as a waste product (lucky for us, since we need it to breathe!). Any green part of a plant can photosynthesise, but leaves are the main photosynthesis factories.

Quick Fact: The oxygen you're breathing right now was probably made by a plant through photosynthesis!

What Plants Do With Their Glucose

Plants don't just make glucose to sit around - they're busy converting it into everything they need to grow and survive. It's like having the ultimate building material that can be transformed into anything!

Some glucose gets used immediately for respiration (plants need energy too!). The rest gets converted into starch for storage - think of it as the plant's emergency food cupboard. Cellulose is made to build strong cell walls, whilst lipids get stored in seeds for future plant growth.

Plants also combine glucose with nitrates from the soil to create amino acids, which then link together to form proteins. It's basically plant biochemistry at its finest - one simple sugar molecule becomes the foundation for everything the plant needs.

The rate of photosynthesis can be measured by tracking oxygen production, CO₂ uptake, or carbohydrate production. Light intensity, CO₂ concentration, temperature, and chlorophyll levels all affect how fast photosynthesis happens.

Remember: When light becomes limiting, plants actually produce more chlorophyll to capture every available photon!

Factors That Control Photosynthesis Rate

Understanding what speeds up or slows down photosynthesis is crucial for everything from growing crops to predicting climate change effects. Think of it like tuning a car engine - multiple factors need to work together perfectly.

Light intensity shows a linear relationship at low levels - more light equals faster photosynthesis. But eventually, the graph levels off because something else becomes the limiting factor. It's like having a bottleneck in a production line.

Carbon dioxide concentration works similarly - increase the CO₂ and photosynthesis speeds up, until another factor becomes limiting. Remember, CO₂ is literally one of the raw materials, so running out slows everything down.

Temperature affects photosynthesis because enzymes control the chemical reactions involved. Too cold and molecular collisions happen too slowly. Too hot and the enzymes get denatured (permanently damaged), causing the rate to crash dramatically.

Exam Tip: Look for the point where graphs level off - that's when a limiting factor kicks in!

Cell Biology - The Building Blocks of Life

Cells are like tiny factories, each with specialised parts doing specific jobs. Knowing the difference between animal and plant cells is fundamental to understanding how life works at the smallest level.

Animal cells contain five key structures: the cell membrane (controls what goes in and out), nucleus (contains DNA and controls everything), cytoplasm (where reactions happen), ribosomes (protein factories), and mitochondria (powerhouses that release energy).

Plant cells have everything animal cells do, plus three extras. The cell wall made of cellulose provides structure and strength. Chloroplasts contain chlorophyll and carry out photosynthesis. The vacuole stores cell sap and waste products - it's like the plant's storage and recycling centre.

Each organelle has evolved to do its job perfectly. Mitochondria are where aerobic respiration happens, ribosomes are the sites of protein synthesis, and chloroplasts make plants green whilst powering photosynthesis.

Memory Trick: Plant cells have "extras" because they need to make their own food and stand upright without a skeleton!

Microscopy and Cell Development

Modern biology wouldn't exist without microscopes - they've opened up the invisible world of cells and shown us how complex life really is at the microscopic level.

Light microscopes are the workhorses of school labs - cheap, easy to use, but limited in resolution (how much detail you can see). Electron microscopes use electrons instead of light, giving 2000 times better resolution but costing a fortune and requiring serious training to operate.

Magnification = image size ÷ actual size. Converting between units is crucial: multiply by 1000 going from mm to μm to nm. Getting this wrong in exams is easily avoidable with practice!

Stem cells are the ultimate multitaskers - they can differentiate into any specialised cell type through mitosis. A zygote (fertilised egg) divides repeatedly, creating embryonic stem cells that eventually become every cell in your body. Diffusion moves particles from high to low concentration, affected by concentration gradient, temperature, and surface area.

Key Point: Resolution matters more than magnification - there's no point making a blurry image bigger!

The Circulatory System - Your Body's Transport Network

Your circulatory system is like a sophisticated delivery service, moving nutrients, oxygen, and waste products around your body 24/7. Understanding how it works reveals why you feel dizzy when you stand up too quickly!

Animals have either open or closed circulatory systems. Insects have open systems where blood flows freely through body cavities, making direct contact with organs. Their blood doesn't carry CO₂ and lacks red blood cells.

Most animals (including humans) have closed systems where blood stays in vessels. Single circulation (like in fish) sends blood from heart to gills to body tissues, but blood pressure drops significantly at the gills. Double circulation (like in mammals) is more efficient - blood goes heart → lungs → heart → body tissues.

The heart has four chambers: thin-walled atria receive blood, whilst thick-walled ventricles pump it out. The pulmonary artery carries blood to lungs, the aorta supplies the body, and valves ensure one-way flow.

Think About It: Double circulation means your heart works twice as hard, but delivers oxygen much more efficiently!

Communicable Diseases - When Pathogens Attack

Communicable diseases spread between people and can seriously disrupt your life. Knowing how they spread and what they do helps you stay healthy and understand public health measures.

Viral diseases like measles cause fever and red skin, potentially leading to blindness and brain damage. There's no treatment, but vaccines prevent infection. HIV/AIDS starts with flu-like symptoms, spreads through sexual contact, and hides in the immune system - no vaccine exists yet, but drugs can manage it.

Bacterial diseases include salmonella $from contaminated food, causing vomiting and diarrhoea 8-72 hours after eating$ and gonorrhoea (sexually transmitted, causing discharge and painful urination, potentially leading to infertility).

Fungal diseases create irritated, scaly, itchy skin and can attack lungs or brain if severe. Malaria is caused by protist pathogens that damage the liver and red blood cells, causing fever and weakness in tropical regions.

Remember: Prevention is always better than cure - vaccines, safe sex, and good hygiene stop most communicable diseases!

Lifestyle and Modern Medical Treatments

Your lifestyle choices today affect your health for decades to come. Understanding the science behind these effects helps you make informed decisions about your body.

Smoking delivers tar (causing cancer), nicotine (highly addictive), and carbon monoxide (poisonous gas) to your lungs. Other chemicals paralyse ciliated cells that normally clear mucus, allowing harmful substances to build up.

Alcohol contains ethanol, which is toxic and affects your nervous system. Short-term effects include blurred vision and slowed reactions, whilst long-term use causes heart disease and other serious health problems.

Organ transplants can save lives but require careful tissue matching to prevent rejection. The immune system sees donated organs as foreign invaders, so immunosuppressant drugs are needed to prevent destruction of the transplanted organ.

Gene therapy involves inserting functioning alleles into cells with faulty genes. Scientists use restriction enzymes to cut out healthy genes, make multiple copies, then insert them into patients with genetic disorders like cystic fibrosis.

Life Tip: Most lifestyle diseases are preventable - the choices you make now determine your future health!

The Digestive System - Breaking Down Your Food

Every bite you take goes on an incredible journey through your digestive system, getting broken down from complex food into simple molecules your body can actually use.

The process starts in your mouth where teeth physically break food down, whilst salivary glands release amylase enzymes. Food travels down the oesophagus to your stomach, where acid and enzymes churn everything into a soup-like mixture.

The liver produces bile (stored in the gallbladder) which isn't an enzyme but helps lipase work effectively by increasing pH and emulsifying fats. The pancreas releases multiple enzymes into the small intestine, where most absorption happens.

Three key enzymes do the heavy lifting: amylase breaks carbohydrates into simple sugars, protease converts proteins into amino acids, and lipase splits lipids into glycerol and fatty acids. The large intestine absorbs water, whilst the rectum stores waste before elimination through the anus.

Amazing Fact: Your small intestine is about 6 metres long but coiled up to fit in your abdomen - that's a lot of surface area for absorption!