Properties and functions of the living cell

Cell nutrition refers to how living cells obtain and use food materials to survive and function properly. Every cell needs nutrients like glucose, proteins, fats, minerals, and vitamins to carry out life activities such as growth, reproduction, and energy production. Cells obtain these nutrients through their cell membranes in a process called absorption.

Think of a Nigerian cassava plant cell: it makes its own food through photosynthesis using sunlight, water, and carbon dioxide. Animal cells, however, cannot make their own food. Instead, they depend on nutrients from the food we eat. When you eat a plate of jollof rice and beans, your digestive system breaks down these foods into tiny particles. Your cells then absorb these nutrients to get energy and build new body tissues.

Without proper nutrition, cells cannot function well and your body becomes weak. This is why eating balanced meals is essential for your health.

**

Autotrophic organisms are living things that make their own food instead of depending on others for it. The word "autotroph" means "self-feeder." These organisms use energy from the sun or chemicals to convert simple inorganic substances like water and carbon dioxide into complex organic food. The two main types are photosynthetic autotrophs, which use sunlight, and chemosynthetic autotrophs, which use chemical energy.

A perfect Nigerian example is the cassava plant growing in your family farm. The cassava plant is autotrophic because it uses sunlight, water from the soil, and carbon dioxide from the air to manufacture its own glucose through photosynthesis. This glucose feeds the entire plant and eventually produces the tubers we harvest and process into gari and fufu.

Photosynthesis is the process where green plants make their own food using sunlight. Think of it as the plant's kitchen! The plant takes in carbon dioxide from the air through tiny holes called stomata, absorbs water through its roots, and when sunlight hits the green chlorophyll in the leaves, magic happens. The plant converts these three ingredients into glucose (sugar) for energy and releases oxygen as a waste product.

Consider a cassava plant growing in a Nigerian farm. During the day, its green leaves capture sunlight and transform it into chemical energy stored in glucose. This glucose helps the plant grow tall, produce leaves, and eventually form the cassava tuber we harvest and eat. Without photosynthesis, there would be no food or oxygen on Earth!

Heterotrophic organisms are living things that cannot make their own food, so they must eat other organisms to survive. When we talk about holozoic nutrition specifically, we mean organisms that ingest solid food—basically, they eat chunks of material and then break it down inside their bodies. Think of a goat grazing in a Nigerian village: it eats grass (solid plant material), swallows it, and its digestive system breaks down that food internally to extract nutrients.

Humans are holozoic heterotrophs too. We eat rice, beans, meat, and vegetables as whole pieces, then our stomach and intestines digest them. Other examples include dogs, chickens, and most animals you see around Nigeria. This is different from parasites or saprophytes, which are heterotrophs but feed differently.

Cellular respiration is the process by which cells break down food molecules to release energy. Think of it like burning fuel in a generator – your body breaks down glucose (a type of sugar) in the presence of oxygen to produce energy in the form of ATP, which powers every activity you do. This happens continuously in your mitochondria, the powerhouse of the cell.

There are two main types: aerobic respiration, which requires oxygen and produces more energy, and anaerobic respiration, which happens without oxygen. When you run hard during a football match in Lagos, your muscles initially use anaerobic respiration, producing lactic acid that causes muscle fatigue.

The equation for aerobic respiration is: Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP). Your body then expels the carbon dioxide through breathing.

Aerobic respiration is the process your body uses to break down glucose (sugar) using oxygen to release energy in the form of ATP. Think of ATP as the "energy currency" of your cells—it's what powers everything you do, from thinking to running to digesting food.

When you eat a plate of jollof rice, your body digests it into glucose. This glucose enters your cells where it's broken down step by step through glycolysis, the Krebs cycle, and the electron transport chain. Each stage releases energy that gets stored in ATP molecules. One glucose molecule can produce up to 38 ATP molecules! This is why aerobic respiration is so efficient compared to anaerobic respiration.

Without this process, your cells would have no energy to function. Every movement, every thought, every heartbeat depends on the ATP produced through aerobic respiration.

Anaerobic respiration is the breakdown of glucose to release energy without using oxygen. Unlike aerobic respiration which requires air, this process happens in oxygen-free environments. Your muscle cells use this during intense exercise when oxygen supply runs low, causing that burning sensation in your legs.

In Nigeria, you see this daily in fermentation processes. Local brewers produce palm wine through anaerobic respiration where yeast cells break down sugars without oxygen, producing alcohol and carbon dioxide as waste products. This same process helps preserve foods like gari and fufu.

The glucose molecule splits into smaller molecules like pyruvate, which then converts to lactate in animals or ethanol and carbon dioxide in microorganisms. Anaerobic respiration releases far less energy than aerobic respiration—only two ATP molecules compared to about thirty-six ATP.

The living cell processes food to release energy needed for all life activities. When you eat a plate of jollof rice, your cells break down the carbohydrates into glucose through digestion. This glucose enters cells where a process called respiration happens. During cellular respiration, glucose is broken down in tiny structures called mitochondria, releasing energy stored in chemical bonds. This energy is captured and stored in a molecule called ATP, which is like the cell's energy currency. Think of it like converting naira notes into smaller denominations you can use for daily purchases. The cell uses this ATP energy for movement, growth, repair, and maintaining body temperature. Without this energy release process, your body cannot function at all.

Excretion is the removal of waste products produced during metabolic activities in living cells. When your body breaks down food for energy, it creates harmful byproducts that must be eliminated. Without excretion, these wastes would accumulate and poison your cells, causing serious damage or death.

Different organisms excrete different wastes. Plants release oxygen as a byproduct of photosynthesis through their stomata—the tiny pores on their leaves. Humans and other animals produce urea from protein breakdown, which the kidneys filter from blood and excrete as urine. Carbon dioxide, produced during respiration in all cells, is exhaled through the lungs.

Think of it like your home's waste management system: just as refuse must be collected and removed from your neighbourhood to prevent disease, cells must eliminate their metabolic waste products to stay healthy and function properly.

Single-celled aquatic organisms like Amoeba and Paramecium living in Nigerian ponds and rivers must remove waste products from their bodies just like you do. These tiny creatures produce carbon dioxide and nitrogenous wastes from their metabolism that would poison them if allowed to build up. Since they lack specialized organs like kidneys, these organisms excrete directly through their cell membrane into the surrounding water. The waste simply diffuses out because it's in higher concentration inside the cell than outside. Amoeba, commonly found in Lagos waterways, also uses contractile vacuoles to collect excess water and expel it, preventing the cell from bursting. This process keeps the organism's internal environment stable and allows it to survive healthily.

Metabolism is all the chemical reactions happening inside living cells to keep us alive. When cells break down food for energy or build new materials, they produce waste products that the body must get rid of. These wastes include carbon dioxide from respiration, which leaves through your lungs when you breathe. Urea is another major waste made when your liver breaks down proteins, and your kidneys filter it into urine. Sweat contains urea and excess salts removed through your skin. Think of a Lagos hawker selling roasted meat—the smoke is like carbon dioxide leaving his body during metabolism. If these wastes accumulated inside cells, they would poison the organism and cause serious damage. The body's ability to eliminate metabolic wastes shows how well-designed living systems truly are.

**

Growth is the permanent increase in size and mass of a living organism through cell division and enlargement. When cells divide during mitosis, they produce more cells, increasing the organism's total volume. Additionally, cells accumulate more cytoplasm and nutrients, making them bigger. Think of a growing Nigerian child – their body continuously produces new cells and enlarges existing ones, making them taller and heavier over time.

In plants, growth occurs through cell division in the meristem regions, allowing roots and stems to extend. A maize plant grows taller because cells in its growing tips constantly divide and expand. In animals, growth happens throughout the body as cells multiply and increase in size until physical maturity is reached.

Growth requires energy from respiration and raw materials like proteins and minerals. This process continues throughout an organism's life but is most rapid during youth.

Growth in living organisms happens because cells divide to create new cells. When a cell becomes too large, it splits into two daughter cells through a process called mitosis. This is how your body grew from a tiny baby to your current size. Think of it like this: if a single cell can only feed and function properly up to a certain size, then dividing creates more cells that can each do their job efficiently.

In Nigeria, when you see a child growing taller and stronger each year, that's cell division happening throughout their body. Their bones, muscles, skin, and organs are all increasing in cell number. Without cell division, growth would be impossible because you'd just have one giant cell trying to keep a whole body alive.

The new cells produced are identical to the parent cell, so they can perform the same functions. This continuous process is why you keep growing until you reach your adult size.

Mitosis is the process where a cell divides to produce two identical daughter cells. This is how your body grows and replaces worn-out cells. When you were a baby, mitosis happened constantly, making you bigger and taller. Even now, your skin cells divide through mitosis to replace dead skin you shed daily—about 30,000 to 40,000 cells every minute!

Enlargement happens when cells increase in size by taking in water and nutrients. Growth combines both processes: cells enlarge first, then divide through mitosis to create more cells. Think of a growing cassava plant in a Nigerian farm. The plant cells enlarge as they absorb water and minerals from the soil, then divide through mitosis, making the plant taller and wider until it's ready for harvest.

Growth is an increase in size and mass of an organism through cell division and enlargement. There are two main aspects: growth in length and growth in mass. When a plant grows taller, its cells divide through mitosis in the meristem regions, especially at the root and shoot tips. This is called indeterminate growth because it continues throughout the plant's life. A mango tree demonstrates this perfectly—it keeps getting taller and wider every year.

In animals, growth is mostly determinate, meaning it stops at adulthood. Human growth involves cell division during childhood and adolescence, then eventually halts. Growth requires proper nutrition because cells need raw materials like proteins and minerals to build new cell structures. Without adequate food, as seen in malnourished children in rural Nigeria, growth becomes stunted.

The difference between growth and development is important: growth is physical increase in size, while development involves changes in structure and function as organisms mature.

The meristematic tissues in plants are the regions where fastest growth occurs. These are special areas containing undifferentiated cells that constantly divide to produce new tissues. Two main regions exist: apical meristems at the tips of roots and shoots, responsible for lengthening the plant, and lateral meristems like the cambium, which increase the plant's thickness. When you observe a growing mango tree in your compound, the tips of new branches extending upward and the trunk becoming thicker both result from meristematic activity. The apical meristem is particularly active during the early stages of plant development. Understanding these growth regions helps explain why plants grow continuously throughout their lives. The cells in meristematic regions are small, densely packed, and metabolically active, making them different from mature cells elsewhere in the plant.

**

Growth hormones are chemical messengers produced mainly by the pituitary gland at the base of your brain. These hormones control how your body grows taller, builds muscles, and develops during puberty. When growth hormone levels are normal, your cells divide properly and you develop at the right pace. During your teenage years, growth hormones work overtime, which is why you notice rapid changes in height and body shape.

Think of it like this: a Nigerian teenager who eats well and sleeps enough produces adequate growth hormones, allowing their body to develop normally. Without sufficient growth hormones, growth becomes stunted. Growth hormones also influence how cells use nutrients and energy, affecting your metabolism and overall health. They work alongside other hormones to regulate cell division and tissue repair throughout your body.

Tropisms are growth movements where plants bend or grow towards or away from external stimuli like light, gravity, or water. These movements help plants survive by positioning themselves optimally in their environment. Phototropism is when plants grow towards light—you've probably noticed how a potted plant on your window sill leans towards the sunlight. This happens because the plant hormone auxin distributes unevenly, causing cells on the shaded side to elongate more than cells on the lit side.

Geotropism is growth in response to gravity, where roots always grow downward and shoots grow upward, regardless of soil position. This is crucial for plants to absorb water and nutrients properly. In Nigeria, if you plant a seed sideways, it will still redirect its root downward and shoot upward within days.

Hydrotropism involves roots growing towards moisture, essential for plant survival in our varying rainfall patterns.

Cell enlargement is the process where a cell increases in size by taking in water and nutrients. When a cell absorbs water through osmosis, its vacuole becomes larger, pushing the cytoplasm outward and making the entire cell bigger. This happens continuously as living organisms grow.

Think of how a maize seedling develops into a tall plant. The cells in the seedling's roots and shoots don't just increase in number through mitosis; each individual cell also enlarges significantly. Water absorption by the large central vacuole is the main reason young maize plants can grow so quickly in size during the rainy season.

Enlargement differs from cell division because one cell becomes larger rather than splitting into two. Without enlargement, your body couldn't grow properly even if cells divided constantly. Both processes work together: cell division increases cell number while enlargement increases cell size, allowing proper growth and development of tissues and organs.

Movement is one of the key characteristics of living things, and it happens at the cellular level too. Cells move in different ways depending on their type and environment. Some cells use structures called cilia and flagella—tiny hair-like projections that beat back and forth to push the cell through liquids. The human sperm cell is a perfect example; it uses its long flagellum to swim through the female reproductive tract to reach the egg. Other cells like white blood cells can change their shape and squeeze through tiny spaces in your body to fight infections. Even plant cells show movement when their cytoplasm flows around inside the cell, a process called cytoplasmic streaming. This internal movement helps distribute nutrients and waste products throughout the cell efficiently.

Cilia and flagella are hair-like structures that help cells move. Cilia are short, numerous extensions on a cell's surface that beat together like tiny oars, creating waves to push the cell or surrounding fluid. Flagella work similarly but are longer and fewer in number, rotating like a propeller to move the cell forward. Think of cilia like many small paddles working as a team, while flagella is like a single powerful tail.

In your body, ciliated cells line your respiratory tract—the tubes in your lungs. When you inhale dust or pollutants in Lagos traffic, these cilia beat upward to push mucus containing the particles out, protecting your lungs. Flagella appear in sperm cells, where the single tail whips side to side to help sperm swim toward the egg during reproduction.

Both structures contain microtubules arranged in a 9+2 pattern and are covered by the cell membrane. Understanding their movement mechanisms is crucial for your exam.

Cyclosis is the continuous circular movement of cytoplasm within a living cell. Think of it like a slow, steady river flowing inside the cell, carrying organelles such as mitochondria, ribosomes, and vacuoles along with it. This movement happens in plant and animal cells, though it's more visible in plant cells because of their larger size and fixed position.

The main purpose of cyclosis is to distribute nutrients, oxygen, and other important substances throughout the cell efficiently. Since some parts of the cell are far from the cell membrane, cyclosis ensures that these interior regions receive what they need to survive and function properly.

You can observe cyclosis clearly in the leaf cells of a water plant like the water hyacinth, commonly found in Nigerian ponds. Watch under a microscope and you'll see the chloroplasts moving in a circular pattern around the cell.

Reproduction is how cells make new cells from existing ones. There are two main types you must know. Mitosis produces two identical daughter cells used for growth and repair of body tissues. This happens in your body cells right now as you grow taller and your wounds heal. Meiosis, on the other hand, produces four genetically different sex cells called gametes—sperm in males and eggs in females. These have half the chromosome number of the parent cell, which is why when sperm meets egg during fertilization, the full chromosome number restores in the new organism. Think of how a Nigerian woman's body produces eggs monthly while a man continuously produces sperm; both use meiosis. These two processes are absolutely different in purpose and outcome, which examiners love testing.

Asexual reproduction means one organism produces offspring without needing another organism. Two main types are fission and budding. Fission happens when a cell or organism splits into two equal parts, each becoming a complete new organism. Bacteria reproduce this way—a bacterium simply divides into two identical daughter cells. Budding is different because a small outgrowth forms on the parent organism, develops into a miniature version, then detaches as a new individual. Yeast cells, which Nigerians use in bread-making, reproduce by budding. You'll see this clearly on prepared slides under the microscope—the bud looks like a tiny bump on the parent cell. Both methods produce genetically identical offspring quickly, which helps organisms survive when conditions are favorable. The advantage is speed; the disadvantage is no genetic variation.

Budding is a type of asexual reproduction where a new organism grows as an outgrowth from the parent's body. Think of it like a child developing while still attached to the parent. In yeast, which is a single-celled fungus used in making bread and palm wine in Nigeria, a small bulge forms on the cell wall. This bulge gradually enlarges, develops its own nucleus, and eventually separates to become an independent yeast cell. Chlamydomonas, a green alga, reproduces similarly by forming buds that detach and grow into new organisms.

This process is quick and efficient because only one parent is needed. The offspring are genetically identical clones of the parent, ensuring rapid population growth under favourable conditions. Unlike sexual reproduction, budding requires no mate-finding or gamete fusion, making it perfect for single-celled organisms.

Conjugation is a special way that some bacteria and single-celled organisms reproduce sexually. During conjugation, two cells come together and exchange genetic material through a tiny bridge called a pilus. Think of it like two people sharing information—one cell acts as the donor, passing DNA to the recipient cell. This process happens commonly in bacteria like E. coli found in our intestines, which is why doctors study how antibiotic resistance spreads between bacteria through conjugation.

The amazing thing about conjugation is that it allows organisms to share beneficial traits, like resistance to antibiotics or ability to digest new food sources. After conjugation, both cells have new genetic combinations, making them genetically different from their parents. This variation helps populations adapt to environmental changes.

Gametogenesis simply means the formation of sex cells called gametes. In Paramecium, a single-celled organism found in stagnant water around Lagos and other Nigerian wetlands, two cells come together and exchange genetic material through a process called conjugation. This is how Paramecium reproduces sexually. Spirogyra, a green algae you'll find in ponds, reproduces through a similar process where two filaments join together and their nuclei fuse, creating a zygote with combined genetic material.

When gametes from two different organisms fuse, they combine their chromosomes to form a diploid cell. This mixing of genes produces variation in offspring, which is crucial for species survival. Unlike asexual reproduction, sexual reproduction through gamete fusion ensures genetic diversity in populations, making organisms stronger and better adapted to environmental changes.

Understanding these processes helps explain how even microscopic organisms ensure their species continue and evolve.