Year 8 Biology Cells Test Revision Guide

1. What is a cell? What are the 3 main components of all cells?

A cell is the smallest, independent unit that makes up all living organisms and the tissues of the body. The three main components are the cell membrane, the nucleus, and the cytoplasm.

2. Explain the difference between prokaryotic and eukaryotic cells? Be able to give an example of each.

Prokaryotic cells are simpler in structure and generally smaller than eukaryotic cells. They are always unicellular, do not contain any organelles that are covered by a membrane, have no distinct nucleus, and their DNA is in the cytoplasm. They can be found in single-celled organisms, such as bacteria. Eukaryotic cells are generally larger and much more complex. They can be either multicellular or unicellular and possess membrane-bound organelles, including a nucleus. They can be found in every multicellular organisms, e.g plants.

3. What are organelles?

Organelles are small, specialised, membrane bound structures found inside cells that perform specific functions (like mini organs). eg mitochondrion.

4. What is a micron?

a micron (µm) is a unit of length used to measure cells - one thousandth of a millimeter.

5. Describe the difference between the following types of microscopes and explain what each one can be used for.

a. light microscope: one that uses sunlight or electric light. They are the most common type of microscope

b. monocular microscope: has one objective lens

c. stereo microscope: provides a 3D image, has 2 eyepiece lenses( used to see whole specimens )

d. compound microscope: has many different objective lenses

e. electron microscope: use a beam of electrons instead of light (used when high magnifications are needed, but you cannot use it on living things )

6. How do you determine the magnification of a microscope?

Multiply the power of the eyepiece lens by the power of the objective lens you are using.

7. What happens to the field of view of a microscope as the magnification increases?

The field of view ( the image you see as you look through the microscope ) gets smaller as you increase the magnification but you can see the specimen in more detail.

8. Explain what the following are and describe what they are used for.

a. slide: A slide is a flat, rectangular piece of glass or plastic used to hold a specimen

b. coverslip: a very thin square or rectangular piece of glass (or plastic) that is placed over the specimen on a microscope slide. It helps flatten the specimen, protects the objective lens, and prevents the specimen from drying out

c. specimen: the object that is being observed

d. wet mount: a specimen that has had water or a dye added to it with a coverslip, this can be used temporarily as it will decay.

9. Be able to label a diagram of a microscope with the following and describe the purpose of each part.

a. eyepiece lens: lens you look through

b. objective lens: lens that determines the magnification

c. revolving nosepiece: used to change between different magnifications

d. barrel: brings light up into the eyepiece

e. stage: Where the slide is placed

f. diaphragm: adjusts the amount of light hitting the specimen

g. arm: used to safely carry the microscope

h. clips: hold slide in place on the stage

i. condenser: focuses the light onto the specimen

10. Be able to a draw a diagram of and explain the function of the following

organelles.

a. cell membrane: a thin, flexible barrier that surrounds the cell that controls what can enter and leave the cell

b. cytoplasm: jelly-like substance that fills the cell, transports organelles and holds nutrients, water and wastes.

c. nucleus: contains the chromosomes, control centre for cell, coordinates all organelles

d. nucleolus: makes ribosomes

e. RER = transports proteins around and out of cell

Smooth ER = makes and transports fats

f. golgi body: package and distribute proteins and other materials produced in the cell.

g. vacuole: store water, waste products, and other materials. They are much larger in plant cells than animal cells and help maintain the cell's shape and structure

h. lysosome: small, spherical organelles that contain digestive enzymes. They break down waste products, dead organelles, and foreign materials that enter the cell

i. mitochondrion: "powerhouse of the cell,", generates energy for the cell

j. centriole: helps the cell reproduce itself

l. chloroplast: contain chlorophyll and absorbs sunlight that is used to make food ( photosynthesis )

m. cell wall: rigid structure that gives support in plant cells

n. ribosomes: manufacture protein

11. Be able to draw a typical example of a plant and an animal cell and explain their similarities and differences.

Animal cells = usually rounded in shape, covered only by a thin cell membrane, if vacuoles are present they are very small, contain lysosomes and centrioles. Plant cells = usually more straight sided and rectangular in shape, contain both a cell membrane and an outer cell wall. Have a large central vacuole, chloroplasts, no lysosomes or centrioles.

12. Outline how fungal cells are similar and different to plant and animal cells.

Fungal cells have a cell membrane and a cell wall. The cell wall is made of a different substance than plant cells ( chitin instead of cellulose ) They do not have chloroplasts. They do have lysosomes and centrioles.

13. Be able to draw and describe the function of the following cells:

Muscle cells = used for movement of bones

Nerve cells = coordinate movement and reactions, thinking

Red blood cells = carry oxygen to body cells

White blood cells = fight bacteria, defend against diseases

Fat cells = store of energy, insulation

Skin cells = protection

Guard cells = open and close pores in leaves to let oxygen and carbon dioxide in and out.

Xylem cells = transport water through plant

Phloem cells = transport food through a plant ( sugar )

Root hair = absorb water from the soil into the plant

Palisade = cells in leaf that photosynthesize and make food for the plant

14. Describe the similarities and difference between sperm cells and pollen

cells.

Both sperm and pollen cells are male reproductive cells. Sperm in animals and pollen in plants. Sperm have only a cell membrane, pollen have both a membrane and a cell wall.

15. Explain how the following relate together by using a simple flow diagram: tissues, cells, organs, organelles, organism, body system.

organelles – cells – tissues – organs – organ systems – organism

16. What is a stem cell? Why are they important?

unspecialised cell that has the potential to develop into a particular kind of specialised cell. They are important because doctors can use them to grow cells that people might need eg replace worn out or diseased brain cells, skin cells, blood cells etc. We may be able to grow new organs eg. for heart transplants.

17. What is the connection between cells and cancer?

cancer is uncontrolled cell growth and reproduction that produces tumours that interfere with healthy cells and use up too much energy.

18. What is Mitosis? Where does it occur and what is its purpose?

Mitosis is a type of cell division in which one cell (the mother) divides to produce two new cells (the daughters) that are genetically identical to itself. Mitosis occurs inside the nucleus of somatic cells in an organism. Somatic cells are all the body's cells except for the sex cells (sperm and egg). The purpose is for growth and to replace damaged cells.

19. Using diagrams describe the different stages of mitosis and use the following terms to describe what is happening in each stage. (chromosomes, chromatids, centromere, spindle, centrioles, cytokinesis, parent cell, daughter cells)

interphase= copy its DNA and centrosome, so the chromosomes in the nucleus each consist of two connected copies, called sister chromatids.

prophase= the chromosomes start to condense (making them easier to pull apart later on). The spindle begins to form, made of microtubules. The spindle grows between the centrosomes as they move apart. The nucleolus disappears.

prometaphase = spindle grows and some of the microtubules begin to capture and organize the chromosomes. The chromosomes become even more condensed and the nuclear envelope breaks down, releasing the chromosomes.

metaphase = spindle has captured all the chromosomes and lined them up at the middle of the cell, ready to divide. All the chromosomes align.

anaphase, the sister chromatids separate from each other and are pulled towards opposite ends of the cell. Each is now its own chromosome.

telophase = the chromosomes begin to decondense and the spindle breaks down.