Class 6 – Science
Explore 30 Class 6 Science topics covering cells, living organisms, plant and animal nutrition, human body systems, transport in plants, adaptations, environment, soil, atmosphere, biodiversity and biological conservation.
🔬 Cells and Organisation of Living Things
Cell as the Structural Unit of Living Organisms
A cell is the basic structural and functional unit of life. All living organisms are made of one or more cells. Some organisms consist of only one cell, while plants and animals contain many specialised cells.
Amoeba is a unicellular organism, whereas a human being is a multicellular organism made of trillions of cells.
What is the difference between a unicellular organism and a multicellular organism? Give one example of each.
The cell is commonly described as the basic unit of life.
Using a Microscope to Study Cells
Most cells are too small to observe clearly with the unaided eye. A microscope magnifies small objects so that structures such as cells can be studied in greater detail.
A thin onion peel can be placed on a glass slide, stained and observed under a microscope to see plant cells.
Identify the eyepiece, objective lenses, stage and focusing controls on a school microscope.
Always handle a microscope carefully and begin observation with a low-power objective when instructed.
Cell Membrane and Its Functions
The cell membrane is a thin boundary surrounding the cell. It separates the contents of the cell from its surroundings and controls the movement of many substances into and out of the cell.
Water, nutrients and waste materials may move across the cell membrane under different conditions.
Why is controlling the movement of substances important for a cell?
The cell membrane helps regulate exchange between the cell and its environment.
Cytoplasm and Cellular Activities
Cytoplasm is the jelly-like material inside a cell between the cell membrane and nucleus. Many cell structures are suspended in it, and numerous chemical reactions necessary for life occur there.
Many reactions involved in releasing and using energy take place within the cell’s internal environment.
Where is cytoplasm located in a typical cell?
Cytoplasm is an active part of the cell, not simply an empty filling.
Nucleus and Its Role in Cells
In typical plant and animal cells, the nucleus contains genetic material and plays an important role in controlling many cellular activities, including growth and reproduction.
Instructions stored in genetic material influence how a cell develops and performs its functions.
Name two important roles associated with the nucleus.
The nucleus contains most of the genetic information in typical eukaryotic cells.
Chloroplasts and Their Role in Plants
Chloroplasts are structures found in many green plant cells. They contain chlorophyll, a green pigment that absorbs light energy used during photosynthesis.
Leaf cells often contain many chloroplasts because leaves receive light and are major sites of photosynthesis.
Why are chloroplasts especially important in green leaves?
Chlorophyll inside chloroplasts helps plants capture light energy.
Vacuoles in Plant and Animal Cells
Vacuoles are membrane-bound compartments used for storage. Mature plant cells commonly contain a large central vacuole filled with cell sap, while animal cells may contain smaller vacuoles.
The large central vacuole of a plant cell contributes to maintaining cell firmness by helping support internal pressure.
How do vacuoles commonly differ between mature plant cells and animal cells?
Vacuoles can store water and dissolved substances.
Organisation from Cells to Organ Systems
In multicellular organisms, specialised cells work together. Similar cells may form tissues, tissues form organs, and organs work together as organ systems.
Cell → Tissue → Organ → Organ System → Organism
Arrange these in correct order: stomach, digestive system, organism, muscle cell, muscle tissue.
Levels of organisation allow specialised parts to cooperate in a multicellular organism.
🌿 Classification and Nutrition
Classification of Living Organisms
Classification is the scientific process of arranging organisms into groups according to shared characteristics and relationships. It helps scientists organise and study the enormous diversity of life.
Animals can be grouped according to characteristics such as body structure, presence of a backbone and other features.
Choose five familiar animals and group them using one clearly stated characteristic.
Scientific classification uses observable characteristics and biological relationships.
Scientific Naming of Organisms
Scientists use internationally recognised scientific names to identify organisms more precisely. In binomial nomenclature, a species name contains two parts: the genus name and the specific epithet.
The scientific name of humans is Homo sapiens.
Homo is the genus and sapiens is the specific epithet.
Why can scientific names be more useful than common names?
Scientific names help scientists communicate about the same species across languages and regions.
Nutrition in Green Plants
Green plants are autotrophs because they can produce organic food from simple raw materials using light energy. They obtain water and minerals from the soil and carbon dioxide from the air.
Roots absorb water from the soil, while carbon dioxide enters leaves through tiny openings called stomata.
List the main materials and conditions a green plant needs for photosynthesis.
Green plants form the base of many food chains because they produce organic food.
Process of Photosynthesis
Photosynthesis is the process by which green plants use light energy to produce glucose from carbon dioxide and water. Oxygen is released as a product.
Carbon dioxide + Water → Glucose + Oxygen
in the presence of light and chlorophyll
Identify the two main raw materials used during photosynthesis and the gas released.
Photosynthesis converts light energy into chemical energy stored in organic molecules such as glucose.
Nutrition in Animals
Animals cannot manufacture food in the same way as green plants. They obtain nutrients by consuming plants, other animals or both. Food must then be processed so useful nutrients can be absorbed.
Cow → Herbivore
Lion → Carnivore
Human → Omnivore
Classify deer, tiger and bear according to their common feeding habits.
Animals are heterotrophs because they obtain organic food from other organisms.
🫀 Human Body Systems
Human Digestive System
The digestive system breaks food into smaller substances that can be absorbed and used by the body. Major organs include the mouth, oesophagus, stomach, small intestine and large intestine.
Mouth → Oesophagus → Stomach → Small Intestine → Large Intestine
Draw and label a simple diagram showing the major parts of the digestive tract.
Much of the absorption of digested nutrients occurs in the small intestine.
Role of Digestive Enzymes
Digestive enzymes are biological catalysts that help break large food molecules into smaller molecules that can be absorbed by the body. Different enzymes act on different types of nutrients.
Amylase helps break down starch into smaller sugars during digestion.
Why must large food molecules be broken into smaller molecules?
Enzymes speed up chemical reactions and are specific in their action.
Human Respiratory System
The respiratory system enables gas exchange between the body and the environment. Air passes through the nose or mouth, down the trachea and through branching airways into the lungs.
Nose/Mouth → Trachea → Bronchi → Smaller Airways → Alveoli
What is the main function of the alveoli in the lungs?
Gas exchange occurs between air in the alveoli and blood in nearby capillaries.
Mechanism of Breathing
Breathing involves inhalation and exhalation. Movements of the diaphragm and rib cage change the volume of the chest cavity, helping air move into and out of the lungs.
The diaphragm contracts and moves downward, and the chest cavity expands.
Exhalation:
The diaphragm relaxes and moves upward as chest volume decreases during normal quiet breathing.
Place a hand on your abdomen and observe its movement during normal inhalation and exhalation.
Breathing is ventilation; cellular respiration is a different chemical process occurring in cells.
Human Circulatory System
The circulatory system transports substances throughout the body. Its major components include the heart, blood and blood vessels.
The heart pumps blood through blood vessels, allowing oxygen and nutrients to reach tissues.
Name the three main types of blood vessels.
Arteries, veins and capillaries perform different roles in circulation.
Components and Functions of Blood
Blood consists of plasma, red blood cells, white blood cells and platelets. These components perform different transport and protective functions.
Red blood cells → transport oxygen
White blood cells → help defend against disease
Platelets → help blood clot
Plasma → transports dissolved substances and blood cells
Match each blood component with its main function.
Blood is a specialised connective tissue with several components.
Human Excretory System
The urinary system helps remove certain metabolic wastes from the blood and regulates water and dissolved substances. The kidneys, ureters, urinary bladder and urethra are its major parts.
Kidneys → Ureters → Urinary Bladder → Urethra
What is the main role of the kidneys in the urinary system?
Excretion removes metabolic waste; it is different from eliminating undigested food from the digestive tract.
🌱 Transport in Plants
Transport Through Xylem
Xylem is vascular tissue that transports water and dissolved mineral ions mainly from the roots toward the stems and leaves. It also contributes to structural support in many plants.
Water absorbed by roots can travel through xylem vessels to leaves, where it is used in photosynthesis and other processes.
What two main materials are transported from roots through xylem?
Xylem is primarily associated with water and mineral transport.
Transport Through Phloem
Phloem transports organic nutrients, especially sugars produced by photosynthesis, between source and sink tissues within a plant.
Sugars produced in mature leaves may be transported to growing roots, fruits or other tissues through phloem.
What is the main difference between materials transported by xylem and those transported by phloem?
Phloem distributes sugars and other organic substances to tissues that need or store them.
🌍 Adaptations and Environment
Adaptations to Terrestrial Habitats
Terrestrial organisms live primarily on land. Their structural, behavioural and physiological adaptations help them obtain resources, cope with temperature changes, conserve water and survive in their particular habitats.
Many desert plants have features that reduce water loss, while camels possess several adaptations suited to dry environments.
List three adaptations that could help an organism survive in a hot, dry desert.
An adaptation is a characteristic that contributes to survival or reproduction in a particular environment.
Adaptations to Aquatic Habitats
Aquatic organisms live in water and possess features suited to freshwater or marine environments. Body shape, respiratory structures and methods of movement can reflect aquatic life.
Many fish have streamlined bodies and fins for efficient movement, and use gills to obtain dissolved oxygen from water.
How does a streamlined body help many aquatic animals?
Aquatic adaptations vary widely because ponds, rivers, oceans and other water habitats have different conditions.
Biotic Components of an Environment
Biotic components are the living parts of an environment. They include plants, animals, fungi, microorganisms and the interactions among them.
Grass, trees, insects, birds, fungi and bacteria are biotic components of many ecosystems.
Observe a garden and list five biotic components you can identify.
“Biotic” refers to living components and their biological influence.
Abiotic Components of an Environment
Abiotic components are non-living physical and chemical factors that influence organisms and ecosystems.
Sunlight, temperature, water, air, rocks, soil and mineral availability are abiotic factors.
How might low rainfall affect organisms living in an ecosystem?
Living organisms interact continuously with both biotic and abiotic parts of their environment.
🌎 Soil, Atmosphere and Biodiversity
Formation of Soil
Soil develops gradually as rocks are weathered into smaller particles and these mineral materials mix with organic matter, water, air and living organisms.
Changes in temperature, moving water, wind, plant roots and chemical processes can contribute to the weathering of rocks.
Why is soil formation generally a slow process?
Soil is a complex natural material, not simply broken rock.
Layers of a Soil Profile
A soil profile is a vertical section through soil showing distinct layers called horizons. The exact horizons present and their thickness vary according to soil type and environmental conditions.
A developed soil may contain organic surface material, topsoil, subsoil, weathered parent material and underlying rock.
Draw a simple soil profile and label the major layers from the surface toward the underlying rock.
Topsoil is often rich in organic matter and biological activity, while deeper horizons differ in composition and structure.
Composition of Earth’s Atmosphere
Earth’s atmosphere is a mixture of gases. In dry air near Earth’s surface, nitrogen and oxygen are the two most abundant gases. Smaller amounts of argon, carbon dioxide and other gases are also present, while water vapour varies with place and time.
Nitrogen → about 78%
Oxygen → about 21%
Argon and other gases → most of the remainder
Carbon dioxide → a small fraction
Which two gases make up most of Earth’s dry atmosphere?
Nitrogen is the most abundant gas in Earth’s atmosphere.
Biodiversity and Biological Conservation
Biodiversity describes the variety of life, including variation among genes, species and ecosystems. Conservation involves protecting biodiversity and using biological resources responsibly.
Protecting habitats, reducing pollution, restoring ecosystems, controlling harmful exploitation and protecting threatened species.
Write three actions that a school or local community could take to help protect biodiversity.
Protecting habitats helps conserve many species at the same time.