Science Number 2

Year 8 Science Revision Notes

Cells and Organelles

1. Definitions:
   i. Cell: The basic unit of life; all living things are made of cells.
   ii. Organelle: A small structure inside a cell that has a specific job (e.g. nucleus, mitochondria).
   iii. Specialised Cell: A cell that has a particular structure or function (e.g. muscle cell, nerve cell).
   iv. Tissue: A group of similar cells that work together to do a job.
   v. Organ: A group of tissues that work together to perform a function (e.g. heart, lungs).
   vi. Organ System: A group of organs that work together (e.g. digestive system).
   vii. Prokaryote: A simple cell without a nucleus (e.g. bacteria).
   viii. Eukaryote: A complex cell that has a nucleus (e.g. plant and animal cells).

2. Comparison of Animal and Plant Cells:

   • Plant cells are often more rectangular.

   • Plant cells have an additional cell wall for protection and stability.

   • Plant cells contain chloroplasts for photosynthesis.

   • Plant cells usually have one large vacuole for waste storage.

   • In contrast, animal cells have multiple small vacuoles, do not have chloroplasts, and lack a cell wall.

3. Role of Organelles:

   Organelle	Function (Job)	Present in Plant, Animal, or Both Cells?
   Nucleus	Controls cell activities, contains DNA	Both
   Mitochondria	Releases energy from food (respiration)	Both
   Cell Membrane	Controls what enters and leaves the cell	Both
   Cell Wall	Provides structure and extra support	Plant
   Cytoplasm	Jelly-like substance where reactions occur	Both
   Chloroplast	Site of photosynthesis	Plant
   Vacuole	Stores water, nutrients, and waste	Both (large in plants)
   Ribosomes	Makes proteins	Both

4. Types of Specialised Cells:
   i. Red blood cell
   ii. Nerve cell (neuron)
   iii. Muscle cell

   • Other acceptable responses could include white blood cell, skin cell, etc.

5. Cell Theory States:
   i. All living things are made of cells.
   ii. Cells are the basic units of life.
   iii. All cells come from pre-existing cells.

Organs and Body Systems

7. Structure and Function Relationship:

   • The structure (shape and design) of a part of the body is related to its function (what it does).

   • Example: The thin walls of alveoli help gases move easily in and out of the blood.

   • Example: The villi and microvilli in the small intestine support quicker nutrient absorption.

8. Ethical Points in Organ Donation and Stem Cell Use:

   • Respect for donor consent.

   • Fair access to organs for all patients.

   • Prevent organ trafficking or exploitation.

   • Responsible use of stem cells for medical research.

   • Balancing benefits of research with respect for human life.

9. Microscopes:

   • Components to label:

     • Eyepiece

     • Base

     • Stage

     • Course adjusting knob

     • Fine adjustment knob

     • Ocular Lens

     • Objective Lens

     • Mirror

     • Arm

     • Nose piece

10. Magnification Table:

    • The ocular lens is always 10x.

    • Missing values for objective lens magnification or total magnification can be calculated based on this information.

11. Gas Exchange During Respiration:

    • Name the two gases exchanged during respiration:

      • Oxygen

      • Carbon dioxide

    • Blood vessels covering the alveoli:

      • Capillaries

12. Size of Alveoli:

    • Alveoli are small to increase the surface area for gas exchange.

13. Organ Systems to Label:

    • Various organ systems need to be identified and labeled in diagrams relevant to human anatomy.

14. Digestive System Function:

    Digestive Organ	Function
    Mouth	Produces bile which helps to break down fats.
    Oesophagus	Absorbs water from undigested food to form solid waste (faeces).
    Stomach	Breaks down food using teeth and mixes it with saliva.
    Small Intestine	Where most digestion and absorption of nutrients take place.
    Large Intestine	A long tube that connects the mouth to the stomach and moves food down by peristalsis (squeezing).
    Liver	Produces digestive juices (enzymes) and insulin, releasing them into the small intestine.
    Pancreas	Mixes food with stomach acid and enzymes to break down proteins.
    Rectum/Anus	Stores and releases faeces.

15. Heart Chambers:

    • Required to label the four chambers of the heart.

16. Comparison of Blood States:

    • Oxygenated Blood: High in oxygen.

    • Deoxygenated Blood: Low in oxygen.

    • Blood that is low in oxygen (deoxygenated) returns from the body and enters the right atrium of the heart. It then moves into the right ventricle, which pumps the blood to the lungs where it picks up oxygen. The blood is now rich in oxygen (oxygenated) and returns to the heart, entering the left atrium. From there, it passes into the left ventricle, which pumps the oxygenated blood out to the rest of the body.

Energy Forms, Transfer, and Transformation

17. Definition of Energy:

    • The ability to do work or cause change.

18. Types of Energy:

    • Kinetic

    • Potential

    • Heat (thermal)

    • Sound

    • Light

    • Any other accepted answers.

19. Comparison of Energy Types:

    • Kinetic Energy: When an object is in motion.

    • Potential Energy: Stored energy (often still).

20. Types of Potential Energy:

    • Gravitational Potential Energy: Stored energy when lifted above the ground (e.g. ball moving).

    • Elastic Potential Energy: Stored energy when an object is stretched or compressed (e.g. stretched elastic band).

21. Energy Transformation:

    • Energy transformation is when energy changes from one form to another.

    • Example: In a torch, chemical energy transforms into light energy.

22. Energy Transfer:

    • Energy transfer is when energy moves from one object to another.

    • Example: Heat transferring from a hot cup to your hands.

23. Law of Conservation of Energy:

    • Energy cannot be created or destroyed; it can only change form or be transferred.

24. Energy Flow Diagrams:

    • Label the energy flow diagrams provided in the materials.

25. Kinetic Energy Calculation Example:

    • A sprinter reaches a top speed of $(12 ext{ m/s})$ during a race.

    • Mass of the sprinter: $(68 ext{ kg})$.

    • Kinetic Energy Formula:
      $KE = rac{1}{2} mv^2$

    • Calculation:
      $KE = rac{1}{2} imes 68 imes 12^2 = rac{1}{2} imes 68 imes 144 = 4896 ext{ J}$

26. Another Kinetic Energy Calculation:

    • A motorcycle with a mass of $(150 ext{ kg})$ moving at a speed of $(22 ext{ m/s})$.

    • Calculation:
      $KE = rac{1}{2} mv^2$
      $KE = rac{1}{2} imes 150 imes 22^2 = 75 imes 484 = 36,300 ext{ J}$

27. Gravitational Potential Energy Calculation Example:

    • A $(2.5 ext{ kg})$ textbook placed on a shelf $(2.0 ext{ m})$ high.

    • Acceleration due to gravity: $(g = 9.8 ext{ m/s}^2)$.

    • Gravitational Potential Energy Formula:
      $GPE = mgh$

    • Calculation:
      $GPE = 2.5 imes 9.8 imes 2.0 = 49 ext{ J}$

28. Gravitational Potential Energy Another Example:

    • A construction worker lifts a $(12 ext{ kg})$ toolbox onto a platform $(1.8 ext{ m})$ high.

    • Calculation:
      $GPE = mgh$
      $GPE = 12 imes 9.8 imes 1.8 = 211.68 ext{ J}$