Diet and Growth Chapter Notes | Physical Education for Grade 8 PDF Download

Nutrients

Carbohydrates, Fats and Proteins

• Carbohydrates, fats, and proteins are essential nutrients found in various foods, each contributing to health and energy needs.
• Rice contains starch, a type of carbohydrate, which the body breaks down into glucose, a sugar used by cells for respiration to release energy.
• Carbohydrates, including starch and sugars, are crucial for providing energy to the body.
• Chicken and beans are rich in protein, which is vital for creating new cells, supporting growth, and repairing damaged tissues.
• Protein is also necessary for producing haemoglobin (which carries oxygen in the blood) and antibodies (which fight infections).
• Avocado contains fats and oils; fats are solid at room temperature, while oils are liquid.
• Fats and oils provide energy and are essential for forming cell membranes.
• Nutrients are substances in food required to maintain health, with protein, carbohydrates, and fats being key examples.

Energy Stores

• The body requires energy continuously, even though food intake is intermittent.
• Carbohydrates and fats are the primary sources of energy, with protein serving as an energy source when carbohydrates and fats are depleted.
• The body stores small amounts of carbohydrates and significant amounts of fat to provide energy when needed.
• Carbohydrates are stored in cells, particularly in the liver and muscles, as short-term energy reserves.
• Fats are stored in special cells under the skin and around organs, serving as long-term energy stores.
• Fat stores also provide heat insulation, which is especially important for animals in cold environments, such as seals, which have thick fat layers to prevent heat loss.

Vitamins

• Vitamins are nutrients needed in small amounts, but their absence can lead to illness.
• Different vitamins are identified by letters (e.g., A, C, D).
• Vitamin A:
  • Essential for healthy vision, particularly for seeing in low-light conditions.
  • Supports white blood cells in fighting pathogens.
  • Deficiency can cause night blindness, where individuals cannot see in dim light.
  • Found in green vegetables, carrots, squash (e.g., pumpkin), fruits, dairy products (e.g., cheese), and certain fish.
• Vitamin C:
  • Helps maintain strong skin and promotes rapid healing of skin damage.
  • Keeps blood vessels and bones healthy.
  • Deficiency leads to scurvy, characterized by weakness and swollen, bleeding gums.
  • Found in fresh fruits and vegetables, especially citrus fruits, potatoes, and colorful berries.
  • Historically, sailors on long voyages developed scurvy due to lack of fresh produce, before vitamin C was understood.
• Vitamin D:
  • Necessary for strong bones and teeth by aiding calcium absorption from food.
  • Found in few foods, with oily fish being the best source.
  • Most vitamin D is produced in the skin when exposed to sunlight.
  • Deficiency, particularly in areas with limited sunlight or among those with minimal sun exposure, can lead to rickets in children, causing abnormal bone growth.

Minerals

• Minerals are essential nutrients, with calcium and iron being particularly important.
• Calcium:
  • Critical for building strong bones and teeth, as these structures contain calcium.
  • Found in dairy products, seeds, and certain nuts (e.g., almonds).
• Iron:
  • Essential for producing haemoglobin, which transports oxygen in the blood.
  • Deficiency causes anaemia, leading to fatigue due to insufficient oxygen transport.
  • Found in red meat, dark green vegetables, fish, shellfish, nuts, and seeds.

Water

• Water is a vital nutrient required daily for various bodily functions.
• Cells and blood contain significant amounts of water, with nearly 90% of body weight attributed to water.
• Water in cells enables chemical reactions by dissolving substances, allowing them to interact.
• Water in blood facilitates its flow, enabling the transport of substances throughout the body.

A Balanced Diet

• A diet consists of the food consumed daily and should include all necessary nutrients and an appropriate amount of energy.
• A balanced diet provides all essential nutrients and matches energy intake to energy expenditure.
• Energy needs vary based on activity levels, genetics, growth, and body size:
  • Active individuals (e.g., those who play sports or walk a lot) require more energy.
  • Sedentary individuals use less energy.
  • Some people’s genes cause their bodies to use energy more quickly.
  • Growing children need extra energy for cell division.
  • Taller individuals use more energy to move than smaller ones.
• Different people require different diets:
  • Growing youths need ample protein for new cells and carbohydrates for energy, plus some fat for energy and cell membranes.
  • Sedentary individuals need less carbohydrates and fats compared to active people.
  • Pregnant women require extra protein for the baby’s cell growth, iron for haemoglobin production, and calcium for bone development.

Fibre

• Fibre is not a nutrient, as it is not digested or absorbed into the blood or cells.
• Fibre passes through the digestive system and is excreted as faeces.
• It is essential for maintaining a healthy digestive system and preventing constipation, where faeces accumulate due to slowed digestion.
• Fibre is primarily cellulose, found in plant cell walls.
• Good sources of fibre include cereal grains, seeds, fresh fruits, and vegetables, which also provide minerals and vitamins.

Food Groups

• Food groups simplify the process of ensuring a diet contains all necessary nutrients.
• Foods can be organized into a food triangle, where the size of each section indicates the proportion of the diet that food group should constitute:
  • Large amounts of fresh fruits and vegetables for minerals, vitamins, and fibre.
  • Plenty of rice, bread, and pasta (preferably whole grain) for starch and fibre.
  • Moderate amounts of meat, fish, eggs, pulses, or dairy products for protein.
  • Small amounts of sweets or fried foods.

Not Too Much

• While all nutrients are necessary, excessive consumption of certain substances should be avoided.
• Too much sugar (a carbohydrate) can lead to tooth decay and increase the risk of diabetes.
• Excessive fat, oil, or carbohydrates can cause weight gain, straining joints, the heart, and other organs.
• Consuming too many animal-derived fats increases the risk of heart disease.

Growth, Development and Health

Growth

• Every human begins life as a single cell, which divides to form two cells.
• Each resulting cell grows and divides again, continuing this process of cell division and growth.
• Initially, all cells are identical, forming a small ball of cells called an embryo, which develops into a baby inside the mother’s body.
• By the time a baby is born, it is a miniature human being, continuing to grow until approximately 18–20 years of age.
• Cells contain significant amounts of protein, which is essential for cell division and growth.
• Energy is required for cells to divide, necessitating a diet rich in protein and sufficient energy for pregnant women and growing children.

Development

• Development encompasses more than just growth; it involves the formation of different tissues and organs as the embryo grows into a baby.
• As a baby develops into a child, leg muscles and bones strengthen, enabling walking and running, while the brain develops, facilitating speech and play.
• Development refers to these progressive changes in structure and function.
• Each individual grows and develops at unique rates and in slightly different ways, but all follow the same developmental stages: baby, toddler, child, adolescent, and adult.
• Developmental stages blend gradually into one another without sharp divisions.

Exercise and Health

• Lifestyle choices, beyond diet, significantly impact health.
• Regular exercise is highly beneficial, helping to burn energy from food and preventing excessive fat storage.
• Exercise strengthens the heart and muscles by making them work harder.
• Engaging in physical activity can also improve mood, fostering a more positive and cheerful outlook on life.

Smoking

• Smoking cigarettes is harmful to both the smoker and those exposed to secondhand smoke.
• Tobacco contains numerous harmful substances, including nicotine, tar, carbon monoxide, and particulates.
• Nicotine:
  • A substance in tobacco smoke that enhances alertness but is highly addictive, making it difficult for smokers to quit.
  • Damages blood vessels, causing them to narrow, which restricts blood flow and increases the risk of heart disease compared to non-smokers.
• Tar:
  • A dark, sticky mixture of substances in tobacco smoke, some of which are carcinogenic (cancer-causing).
  • Increases the risk of various cancers, including lung cancer, by causing cells to divide uncontrollably and spread.
• Carbon Monoxide:
  • A poisonous gas that binds to haemoglobin in red blood cells, preventing it from carrying oxygen to body cells.
  • Reduces the oxygen available for respiration, leading to insufficient energy production in cells.
• Particulates:
  • Tiny particles of carbon and other materials in tobacco smoke that become trapped in the lungs.
  • Cause the breakdown of alveolar walls, reducing the number of tiny alveoli and creating larger spaces, which impairs oxygen absorption into the blood.

Moving the Body

The Skeleton

• The human skeleton, located inside the body, is made of bones and supports the body, unlike the external exoskeleton of insects and arthropods.
• Bones are hard and strong, containing significant amounts of calcium, which is essential for proper bone growth.
• Insufficient dietary calcium can impair bone development.
• Bones are composed of living cells, requiring protein in the diet to build and maintain strength.

Joints

• Joints are the points where two bones meet, allowing movement since bones themselves cannot bend.
• Hinge Joints:
  • Function like door hinges, permitting movement in one direction (back and forth).
  • Examples include the elbow and finger joints.
• Ball-and-Socket Joints:
  • Allow movement in a complete circle, with one bone having a ball-shaped end that fits into a cup-shaped socket in the other bone.
  • The shoulder joint is an example.
• The arm contains several joints, including the shoulder (ball-and-socket), elbow (hinge), wrist, and finger joints, visible in X-rays alongside bones like the humerus, radius, and ulna.

Muscles

• Muscles, composed of specialized cells, move bones at joints by contracting (shortening).
• Muscle contraction requires energy, primarily derived from glucose through respiration, with increased contraction demanding more glucose.
• Muscles are attached to bones via tendons, tough cords that transmit the pulling force of contracting muscles to move bones at joints.
• The biceps muscle, attached to the scapula and radius by two tendons, is a key muscle for arm movement.
• The triceps muscle, longer and thinner, is attached to bones by three tendons and also facilitates arm movement.

Bending the Elbow Joint

• Bending the arm at the elbow involves the biceps muscle contracting and the triceps relaxing.
• The brain sends an electrical impulse via a neuron to the biceps, triggering its cells to contract, shortening the muscle.
• The biceps, fixed to the scapula and radius, pulls these bones closer together when it shortens, bending the elbow.
• The contracting biceps exerts a pulling force through a tendon, moving the radius upward.

Straightening the Elbow Joint

• Straightening the arm at the elbow requires the triceps muscle to contract while the biceps relaxes.
• Muscles can only pull, not push, so the biceps cannot straighten the arm; the triceps is needed for this action.
• The contracting triceps pulls on a tendon, moving the ulna downward to straighten the elbow.
• Muscles either contract to generate force or relax when not in use.

Antagonistic Muscles

• The biceps and triceps work together as antagonistic muscles, coordinating to move the arm at the elbow joint.
• To bend the arm, the biceps contracts while the triceps relaxes, pulling the bones in one direction.
• To straighten the arm, the triceps contracts while the biceps relaxes, pulling the bones in the opposite direction.
• Antagonistic muscles operate in pairs, with one muscle’s contraction causing movement in one direction and the other’s contraction causing movement in the opposite direction.