Year 10 Science Cell Topic Exam Prep

Fundamental Cell Structures: Animal and Plant Cells

  • Animal Cell Components and Functions:

    • Nucleus: Contains the genetic material (DNA/chromosomes) and controls the activities of the cell.
    • Cytoplasm: A jelly-like substance where most chemical reactions happen. It contains enzymes which control these chemical reactions.
    • Cell Membrane: Holds the cell together and controls what goes in and out (semi-permeable).
    • Mitochondria: These are the sub-cellular structures where most of the reactions for aerobic respiration take place. Respiration transfers energy that the cell needs to work.
    • Ribosomes: These are where proteins are made in the cell (protein synthesis).

  • Plant Cell Components (Unique to Plants):

    • Cell Wall: A rigid structure made of cellulose. It supports and strengthens the cell.
    • Permanent Vacuole: Contains cell sap, a weak solution of sugar and salts, which helps keep the cell turgid.
    • Chloroplasts: These are where photosynthesis occurs, which makes food for the plant. They contain a green substance called chlorophyll, which absorbs the light needed for photosynthesis.

Specialized Cells and Their Adaptations

  • Specialized Animal Cells:

    • Sperm Cells (Reproduction): Adapted for swimming to the egg. They have a long tail and a streamlined head. They contain many mitochondria to provide the energy needed for movement and carry enzymes in their head to digest through the egg cell membrane.
    • Nerve Cells (Rapid Signaling): Long to cover more distance and have branched connections (dendrites) at their ends to connect to other nerve cells and form a network throughout the body.
    • Muscle Cells (Contraction): Long (so they have space to contract) and contain lots of mitochondria to generate the energy needed for contraction.

  • Specialized Plant Cells:

    • Root Hair Cells (Absorbing Water and Minerals): Located on the surface of plant roots, which grow into long hairs that stick out into the soil. This gives the plant a big surface area for absorbing water and mineral ions from the soil.
    • Phloem and Xylem Cells (Transporting Substances): Form phloem and xylem tubes, which transport substances such as food and water around plants. To form the tubes, the cells are long and joined end to end. Xylem cells are hollow in the centre and phloem cells have very few subcellular structures, so that stuff can flow through them.

Microscopy and Parts of a Microscope

  • Key Parts of a Light Microscope:

    • Eyepiece: The part you look through; it usually has a magnification of ×10\times 10.
    • Objective Lenses: Usually three or four lenses with different magnifications (e.g., ×4\times 4, ×10\times 10, and ×40\times 40).
    • Stage: The flat platform where the slide is placed.
    • Clips: Used to hold the slide in place.
    • Light Source/Mirror: Directs light up through the specimen.
    • Coarse Adjustment Knob: Used for initial focusing at low power.
    • Fine Adjustment Knob: Used for precision focusing at high power.

  • Calculations in Microscopy:

    • Total Magnification=Eyepiece Lens Magnification×Objective Lens Magnification\text{Total Magnification} = \text{Eyepiece Lens Magnification} \times \text{Objective Lens Magnification}
    • Magnification=Image sizeReal size\text{Magnification} = \frac{\text{Image size}}{\text{Real size}}
    • Units of measurement often involve micrometers (μm\mu m), where 1 mm=1000 μm1\,mm = 1000\,\mu m.

Chromosomes and DNA

  • Genetic Material Structure:
    • DNA (Deoxyribonucleic Acid): The chemical that makes up the genetic material. It is a polymer made up of two strands coiled together in the shape of a double helix.
    • Chromosomes: Found in the nucleus of a cell. Chromosomes are coiled up lengths of DNA molecules. Each chromosome carries a large number of genes.
    • Genes: A small section of DNA found on a chromosome. Each gene codes for a particular sequence of amino acids which are put together to make a specific protein.

Mitosis and the Cell Cycle

  • The Process of Mitosis:

    • Interphase: Before the cell divides, it has to grow and increase the amount of subcellular structures such as mitochondria and ribosomes. It then duplicates its DNA so there’s one copy for each new cell.
    • Prophase: The chromosomes condense and the nuclear membrane breaks down.
    • Metaphase: The chromosomes line up at the center (equator) of the cell.
    • Anaphase: Cell fibers pull the chromosomes apart. The two arms of each chromosome go to opposite ends of the cell.
    • Telophase: Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells—the nucleus has divided.
    • Cytokinesis: The cytoplasm and cell membrane divide, producing two new daughter cells. These daughter cells are genetically identical to the parent cell.

  • Mitosis in Onions (Onion Root Tip Experiment):

    • Onion root tips are used to observe mitosis because they are areas of rapid growth (meristems).
    • A stain (like ethanoic orcein) is often used to make the chromosomes visible under the microscope.
    • The "magic" of mitosis in onions reveals clearly visible stages of chromosome separation due to the lack of complex tissue overlapping at the tip.

Human Reproduction

  • Male Reproductive System: Contains the testes (produce sperm), scrotum, sperm duct, and penis.
  • Female Reproductive System: Contains the ovaries (produce eggs), oviducts (fallopian tubes), uterus (womb), and vagina.
  • Key Processes:
    • Gametes: Sex cells (sperm and egg) that contain half the number of chromosomes (n=23n = 23 in humans).
    • Fertilization: The fusion of the nucleus of a male gamete with the nucleus of a female gamete to produce a zygote.
    • Zygote/Embryo: The zygote divides by mitosis to form a ball of cells called an embryo, which implants in the uterus wall.