Science Assessment 2 Year 7

International symbols are used for elements to ensure consistency and understanding worldwide, regardless of language. These symbols, often from Latin, help scientists easily identify elements like oxygen (O) or gold (Au).

Different elements can chemically join together to form compounds. When elements combine in specific proportions, their atoms bond, creating a new substance with unique properties. For example, hydrogen and oxygen bond to form water (H₂O), which is a compound.

Pure substances consist of only one type of particle. This could be:

• An element: A substance made up of only one type of atom (e.g., gold, oxygen).

• A compound: A substance made of two or more different types of atoms chemically bonded (e.g., water, carbon dioxide).

Mixtures, on the other hand, consist of more than one type of element or compound. These substances are physically combined, not chemically bonded, meaning they can be separated by physical methods. For example, air is a mixture of different gases like nitrogen and oxygen.

Particle-Level Description:

• Elements: Made of identical atoms. The atoms are all of one type and can exist as individual atoms (e.g., helium) or as molecules (e.g., O₂ for oxygen).

• Compounds: Made of molecules that contain two or more different types of atoms chemically bonded together in a fixed ratio (e.g., H₂O has two hydrogen atoms and one oxygen atom). The atoms are arranged in specific ways depending on the compound.

• Mixtures: Contain a variety of different atoms and/or molecules that are not chemically bonded. These particles are simply mixed together and can be separated. For example, in a mixture of salt and water, the salt and water molecules remain separate.

This difference in bonding and particle arrangement explains why elements and compounds are pure substances, while mixtures can contain a variety of particles without forming new substances.

1. Living things are made up of cells:

• Cells are the basic building blocks of all living organisms. Some organisms are made of one cell (unicellular), while others are made of many cells (multicellular).

2. Each cell has different parts called organelles:

• Organelles are specialized structures within cells that perform specific functions to keep the cell alive.

3. Functions of key organelles:

• Nucleus: Controls the cell’s activities and contains the genetic material (DNA).

• Cytoplasm: The jelly-like substance where chemical reactions happen, and organelles are suspended.

• Vacuole: Stores water, nutrients, and waste products. In plants, the vacuole is large and helps maintain structure.

• Cell membrane: A thin, flexible barrier around the cell that controls what goes in and out.

• Chloroplast (only in plant cells): Contains chlorophyll, which helps the plant make food through photosynthesis.

• Mitochondria: The "powerhouse" of the cell, where energy is produced through cellular respiration.

4. Comparison of plant and animal cells:

• Plant cells:

  • Have a cell wall for structure and protection.

  • Contain chloroplasts for photosynthesis.

  • Have a large, central vacuole.

• Animal cells:

  • Do not have a cell wall, only a cell membrane.

  • No chloroplasts (since animals do not perform photosynthesis).

  • Typically have smaller vacuoles.

5. Word equation for photosynthesis:

• Photosynthesis (in plants):

  • Carbon dioxide + water → glucose + oxygen

  • (This occurs in the chloroplasts with the help of sunlight).

6. Word equation for cellular respiration:

• Cellular respiration (in both plants and animals):

  • Glucose + oxygen → carbon dioxide + water + energy

  • (This happens in the mitochondria to release energy).

7. Difference between unicellular and multicellular organisms:

• Unicellular organisms: Made of a single cell (e.g., bacteria, amoeba). They perform all life processes within that one cell.

• Multicellular organisms: Made of many cells that work together (e.g., humans, plants). Different cells have specialized functions.

8. Unicellular organisms reproduce asexually by cell division:

• Asexual reproduction in unicellular organisms (like bacteria) occurs through cell division (mitosis), where one cell splits into two identical cells.

. What is classification, and why is it important?

• Classification is the process of sorting living things into groups based on their similarities and differences.

• It helps scientists understand relationships between organisms, make sense of the diversity of life, and communicate clearly.

• How do we classify? Scientists group organisms based on their structural features, such as body shape or how they move, and by looking at their habitats.

2. Characteristics of living things (MRS GREN):

• Movement: All living things move in some way, even plants.

• Respiration: The process of breaking down food for energy.

• Sensitivity: Ability to sense and respond to their environment.

• Growth: All living things grow and develop.

• Reproduction: Ability to produce offspring.

• Excretion: Removing waste from the body.

• Nutrition: Taking in and using food for energy and growth.

3. How living things are classified:

• Living things are grouped based on their structure (e.g., body parts like bones or wings) and habitats (where they live).

• Different groups show patterns of similarities (things in common) and differences.

4. Definitions of key terms:

• Vertebrate: An animal with a backbone (e.g., humans, fish).

• Invertebrate: An animal without a backbone (e.g., insects, jellyfish).

• Exoskeleton: A hard outer covering that protects the body (e.g., crabs, beetles).

• Endoskeleton: An internal skeleton made of bones or cartilage (e.g., humans, dogs).

• Endothermic: Animals that regulate their own body temperature (warm-blooded), like mammals and birds.

• Ectothermic: Animals whose body temperature changes with the environment (cold-blooded), like reptiles and amphibians.

5. Classification hierarchy:

• Kingdom → Phylum → Class → Order → Family → Genus → Species

• This sequence helps scientists organize living things from broad groups (Kingdom) down to specific types (Species).

6. Types of keys used to classify:

• Dichotomous keys are tools used to identify organisms by answering a series of yes/no questions.

• There are different types of keys, such as branching keys (flowchart style) or numbered steps.

7. Interpreting data with classification keys:

• To use a dichotomous key, you follow the questions step by step, choosing between two options (e.g., Does the animal have wings? Yes or No?) until you reach the correct identification.

8. Constructing a simple dichotomous key:

• Start with broad characteristics (e.g., "Does it have legs?") and work down to more specific traits.

• Make sure each step offers only two choices.

For example, to classify animals:

1. Does it have wings?

   • Yes: Go to step 2.

   • No: Go to step 3.

2. Is it a bird?

   • Yes: It’s a bird.

   • No: It’s an insect.

3. Does it have fur?

   • Yes: It’s a mammal.

   • No: It’s a reptile.

This helps you organize and classify different organisms based on their features.

. What is a force?

• A force is something that changes an object's motion. It can make an object go faster, slower, or change direction.

• A force can be a push, pull, or twist.

2. Types of forces:

• Contact forces: These happen when objects touch each other (e.g., pushing a door).

• Forces that act at a distance: These happen without objects touching (e.g., gravity, magnetic forces).

3. Measuring force:

• The unit of force is the newton (N).

• A spring balance is used to measure the size of a force.

4. Balanced vs. Unbalanced forces:

• Balanced forces: When forces acting on an object are equal and opposite, the object doesn't change its motion.

• Unbalanced forces: When forces are unequal, the object changes motion (it starts moving, stops, or changes speed/direction).

5. Resultant force:

• The resultant force is the overall force when more than one force acts on an object. It has both a size and a direction.

• If forces are unbalanced, the direction of the resultant force will be the same as the object's acceleration (how quickly it speeds up or slows down).

6. Unbalanced force:

• An unbalanced force causes a change in an object's motion (starting, stopping, or changing speed/direction).

7. Friction:

• Friction is a contact force that slows down or stops an object’s motion. It happens when two surfaces rub against each other.