Animal & Plant Cells

Ever wondered what makes up the tiny building blocks of your body? Let's explore cells - the microscopic units of life!

Animal cells are roughly round structures containing several key components. The nucleus acts as the control center, housing DNA and directing all cellular activities. Surrounding this is the cytoplasm, a jelly-like substance where chemical reactions occur. The cell membrane forms the outer boundary and controls what enters and exits the cell.

Animal cells also contain mitochondria (tiny structures for energy production through respiration), small temporary vacuoles $fluid-filled spaces$, and ribosomes (which help make proteins).

Plant cells share many features with animal cells but have some important differences. They have a rigid cell wall made of cellulose that provides support and structure. Plant cells also contain chloroplasts which capture light energy for photosynthesis, and typically have a large, permanent vacuole that helps maintain rigidity.

Quick Fact: Plant cells can be recognized by their rectangular shape, cell walls, chloroplasts, and large vacuoles - all features that animal cells don't have!

Specialised Cells & Microscopy

Your body contains trillions of cells, but they're not all the same! Many cells have adapted for specific functions.

Sperm cells have a streamlined design perfect for their job - fertilising an egg. They feature an acrosome (helps break through the egg cell membrane), a haploid nucleus (containing half the genetic material needed), mitochondria (provides energy for swimming), and a tail for movement. Egg cells, meanwhile, have their own haploid nucleus and a special membrane that allows one sperm to enter before sealing.

When sperm and egg unite, fertilisation occurs - creating a zygote with a complete set of chromosomes (diploid). This single cell will eventually develop into a complete organism!

To study cells, scientists use microscopes. Light microscopes are relatively inexpensive and easy to use but have limited magnification (about 1,500×) and resolution (ability to distinguish between close objects). Electron microscopes offer much higher magnification (up to 500,000×) and resolution by using electron beams instead of light, but they're expensive and require special preparation techniques.

Remember: Magnification tells you how many times larger the image is than the actual object. You can calculate it using the formula: Magnification = Image size ÷ Actual size.

Cell Transport & Enzymes

Cells are constantly moving materials in and out - but how do they do it? Let's find out!

Diffusion is the movement of particles from areas of high concentration to areas of low concentration. It's how oxygen moves from your lungs into your bloodstream and how carbon dioxide moves out. No energy is required - it just happens naturally!

Osmosis is a special type of diffusion involving water molecules moving across a partially permeable membrane. Water always moves from regions of high water concentration to regions of lower water concentration. This is crucial for plants to absorb water through their roots.

Sometimes cells need to move substances against concentration gradients (from low to high concentration). This requires energy and is called active transport. Plant root hair cells use active transport to absorb mineral ions from the soil.

Enzymes are special proteins that act as biological catalysts, speeding up reactions in your body without being used up themselves. They work using a lock and key mechanism - each enzyme has a specific shape that only fits certain substrate molecules. Digestive enzymes like amylase (breaks down starch), protease (breaks down proteins), and lipase (breaks down fats) are vital for turning your food into usable nutrients.

Cool Fact: Without enzymes, most biochemical reactions would happen too slowly to support life!

Health & Disease

What does it mean to be truly healthy? It's more than just not being sick!

According to the World Health Organization, health is "a state of complete physical, mental and social well-being." Physical wellbeing involves being free from disease, getting enough sleep, eating properly, and exercising regularly. Mental wellbeing includes feeling good about yourself and having confidence. Social wellbeing relates to your relationships with others and your ability to interact positively.

Diseases can be classified as either communicable or non-communicable. Communicable diseases are caused by pathogens $disease-causing microorganisms$ and can spread from person to person. There are four main types of pathogens: viruses (like HIV and Ebola), bacteria (like those causing cholera), fungi (like Ash Chalara Dieback in plants), and protists.

Your body has impressive defences against pathogens. Physical barriers include your skin (which forms a tough outer layer), cilia (tiny hairs that trap particles in your airways), mucus (which traps pathogens), and stomach acid (which kills most pathogens). Chemical defences include lysozyme, an enzyme in tears and saliva that kills bacteria.

Did you know? A single sneeze can release up to 40,000 droplets containing pathogens, which can travel at speeds up to 100 miles per hour!

Lifestyle & Health

The choices we make every day can have huge impacts on our health - both good and bad!

Malnutrition occurs when your diet provides inadequate or excessive nutrients. Consuming too many calories from fats and sugars can lead to obesity, while not getting enough of specific nutrients causes deficiency diseases. For example, lack of protein can cause kwashiorkor (swollen belly, small muscles), insufficient vitamin C leads to scurvy (bleeding gums, lost teeth), and inadequate iron causes anaemia (tiredness, difficulty breathing).

Lifestyle choices like consuming alcohol and smoking tobacco can seriously damage health. Alcohol is a depressant drug with short-term effects (poor balance, impaired judgment) and long-term consequences including cirrhosis (liver scarring) and brain damage. Smoking introduces harmful substances like nicotine (addictive), tar (damages lung cilia), and carbon monoxide (reduces oxygen transport in blood).

These habits significantly increase the risk of cardiovascular disease (CVD) - problems affecting the heart and blood vessels. Too much fat in the diet can lead to fatty deposits in arteries, while smoking doubles the risk of CVD. Treatments include lifestyle changes (more exercise, stopping smoking), medications to reduce blood clotting, stents (to widen narrowed blood vessels), or bypass surgery.

Important: Your BMI (Body Mass Index) is calculated using your weight and height $BMI = weight in kg ÷ height in m²$ and can indicate if you're underweight, healthy weight, overweight, or obese.

Inheritance & Genetics

The colour of your eyes, the shape of your nose - these features were passed down to you from your parents through inheritance!

Your body cells contain chromosomes in their nuclei - thread-like structures made of DNA that carry genetic information. Each human body cell has 46 chromosomes arranged in 23 pairs - one chromosome in each pair from your mother and one from your father.

Along each chromosome are sections called genes, which control the development of specific characteristics. For each gene, you might have identical versions (homozygous) or different versions (heterozygous) from each parent. These different versions of genes are called alleles.

Some alleles are dominant (usually shown with capital letters like 'B'), meaning they always show up if present. Others are recessive (shown with lowercase letters like 'b') and only appear if you have two copies. For example, if brown eyes (B) are dominant over blue eyes (b), someone with the genotype Bb would have brown eyes.

Your biological sex is determined by special sex chromosomes - females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The Y chromosome, which comes from the father, contains genes that trigger male development.

Fascinating Fact: You share about 99.9% of your DNA with every other human on Earth. The 0.1% difference accounts for all the variation we see in humanity!

Variation & Genetic Disorders

Look around your classroom - everyone looks different! This diversity is called variation, and it comes from two main sources.

Genetic variation results from the genes we inherit from our parents. Eye colour, blood type, and natural hair colour are examples of genetically determined traits. Environmental variation comes from our surroundings and experiences - like language spoken or scars from injuries. Many characteristics, such as height and skin colour, are influenced by both genetics and environment.

Variation can be continuous (showing a range of values, like height) or discontinuous (having distinct categories, like blood type). This variation arises through sexual reproduction, which involves the fusion of specialized sex cells (gametes) - sperm from males and eggs from females. These gametes are haploid, meaning they have just one set of chromosomes. When they join during fertilization, they form a diploid zygote with a full set of chromosomes.

Sometimes, genes contain mutations that can cause genetic disorders. Cystic fibrosis is an example of a disorder caused by a recessive allele - you need to inherit two copies of the faulty allele to develop the condition. People with just one copy are called carriers; they don't have the disorder but can pass the allele to their children.

Think about this: The endless combinations of genes possible during sexual reproduction mean that (except for identical twins) no two humans who have ever lived or will ever live are genetically identical!

Genetic Diagrams & The Human Genome

Scientists use special diagrams to track how genes are inherited - like predicting what your children might look like!

Genetic diagrams (sometimes called Punnett squares) help predict the possible genetic combinations in offspring. For example, if we cross a tall pea plant (TT) with a dwarf pea plant (tt), all the offspring would have the genotype Tt and the phenotype (physical appearance) of tall plants, because T (tallness) is dominant over t (dwarfism).

One of the most significant scientific achievements of recent times is the Human Genome Project. Completed in 2003, this international effort mapped all 3.3 billion base pairs in human DNA. Scientists from many countries worked together to identify and locate every human gene.

The results of this project have revolutionized medicine. Doctors can now better diagnose genetic disorders, predict disease risks, and determine which treatments will work best for specific patients. Interestingly, over 99% of DNA sequences are identical in all humans - our genetic differences are found in less than 1% of our DNA!

Understanding your genetic makeup could help you make informed decisions about your health in the future. For instance, if you learned you had a higher risk for a particular disease, you might adjust your lifestyle or undergo regular screening to catch problems early.

Amazing Discovery: The Human Genome Project found that humans have approximately 20,000-25,000 genes - far fewer than scientists initially expected!