GCSE Biology Topic 1

How do we calculate the total magnification of a microscope?

Eyepiece lens x Objective lens magnifying power

State the equation that links magnification, image size and actual size.

Image Size = Actual Size x Magnification

Define 'resolution'.

The ability to distinguish between two separate points that are very close together

Which type of microscope has higher magnification and resolving power - Light or electron?

Electron microscopes

Why does the tissue sample need to be stained before looking at it under the microscope?

To visualise/see structures clearly

Which objective lens should we start using?

Low power objective lens

Which focus knob should be used during low and medium power magnification?

Coarse focus knob

Which focus knob should be used during high power magnification?

Fine focus knob

Why must we not use the coarse focus knob during high power magnification?

It moves the stage by too much, may break the lens and the slide

What is the function of a scale bar?

To allow us to calculate the actual size of the sample using I=AM

State the function of the nucleus.

Controls all activities of the cell, contains genetic information

State the function of the cytoplasm.

Site for chemical reactions to take place

State the function of the cell membrane.

Controls what substances go in and out of the cell

State the function of the mitochondria.

Site of aerobic respiration, releasing energy

State the function of the ribosomes.

Site of protein synthesis

State the function of the cell wall.

Strengthens the cell, provide support

State the function of the chloroplasts.

Contain chlorophyll, absorb light to do photosynthesis

State the function of the permanent vacuole.

Contains cell sap to keep plant cells rigid, provide support

State three differences between animal and plant cells.

Plant cells have chloroplasts, permanent vacuole and cellulose cell wall. Animal cells do not

What substance makes up plants' cell walls?

Cellulose

Convert 5mm to µm.

5000µm

State a key difference between prokaryotes and eukaryotes.

Prokaryotes do not have a nucleus. Eukaryotes do.

State one organism that is prokaryotic.

Bacteria

Prokaryotes have a cell wall. True or false?

TRUE

Some bacteria have an extra layer on top of their cell walls. What is the name of that layer?

Slime capsule

Where does the genetic material of a prokaryotic cell exist?

Cytoplasm

What is a difference between prokaryotic and eukaryotic DNA?

Prokaryotic DNA is circular; Eukaryotic DNA is linear

What is the name of extra small DNA rings found in some prokaryotes?

Plasmid

What is the function of flagella?

To allow the cell to swim and move around

State a difference between animal cells and bacteria.

A: No cell wall and plasmid, linear DNA; B: Cell wall and plasmid, circular DNA

State a similarity between plant cells and bacterial cells.

Both have cell walls (but different material)

What is the function of the slime capsule?

Protect the cell

Explain the use of a tail in sperm cells.

To swim and move around (to reach the egg)

Why do sperm cells have lots of mitochondria?

To provide lots of energy for swimming

What is the structure of a sperm cell that contains digestive enzymes to break down the surface of an egg cell?

Acrosome

Describe the adaptations of a nerve cell.

Lots of dendrites; Long axon

What is the function of a nerve cell?

Carry electrical impulses

How does having a long axon help neurones with their function?

Carry electrical impulses over long distances

Describe how a muscle cell is adapted for its function.

Special proteins for contraction; Many mitochondria for energy; Store glycogen to release glucose for respiration

Root hair cells have lots of mitochondria to release energy. What is the energy used for?

Active transport of mineral ions into root hair cells

How do the extensions in root hair cells help with their function?

Increase surface area for efficient water absorption

What is another name for photosynthetic cells in plants?

Palisade mesophyll cells

How are photosynthetic cells adapted for photosynthesis?

Lots of chloroplasts with chlorophyll to absorb light

Which specialised cell in plants make up the tissue for transporting water?

Xylem cells

Name the substance found in xylem cells that allows the cells to withstand high water pressure.

Lignin

State a difference in structure between xylem and phloem.

X: dead, hollow tube, has lignin; P: living, has sieve plates, no lignin

Name the cell that keeps phloem alive.

Companion cells

Define 'diffusion'.

Net movement of particles from an area of high to low concentration (down concentration gradient)

What does it mean by 'net movement'?

Overall movement: particles can move in any direction, but generally speaking, most of the particles are moving in one particular direction, hence 'net' movement

State three factors that affect the rate of diffusion.

Concentration gradient, temperature, surface area

How does concentration difference affect the rate of diffusion?

Higher conc difference/Steeper conc gradient --> faster diffusion

Explain why a higher temperature results in faster diffusion.

More kinetic energy, particles move around more

Name a substance that diffuses into our cells for use.

Oxygen, glucose

Name a substance that diffuses out of our cells to be removed.

Carbon dioxide, urea

Name a structure in the body that is adapted to increase diffusion rate.

Alveoli, villi

Define 'osmosis'.

Net movement of water molecules down the water concentration gradient through a partially permeable membrane

Define 'dilute'.

A solution with a high water conc, but low solute conc

Define 'concentrated'.

A solution with a low water conc, but high solute conc

What are partially permeable membranes?

Membranes that only allow some types of substances to pass through

What is an isotonic solution?

A solution with the same solute conc as the cell

What is a hypertonic solution?

A solution with a higher solute conc than the cell

What is a hypotonic solution?

A solution with a lower solute conc than the cell

If a cell is in a hypertonic solution, water will ___ (enter/leave) the cell.

Leave

If a cell is in a hypotonic solution, water will ___ (enter/leave) the cell.

Enter

What will happen to an animal cell if it is in a hypertonic solution?

Water leaves cell --> shrivelled

What will happen to an animal cell if it is in a hypotonic solution?

Water enters cell --> burst

Why do animal cells burst in hypotonic solutions?

No cell wall

What will happen to a plant cell if it is in a hypertonic solution?

Water leaves cell --> plasmolysed

What will happen to a plant cell if it is in an isotonic solution?

No net water movement --> flaccid

What will happen to a plant cell if it is in a hypotonic solution?

Water enters cell --> turgid

What does 'plasmolysed' mean?

The cell membrane becomes detached from cell wall

Why does the potato skin needs to be removed before putting the potato cylinders into the solutions?

Skin is impermeable

How do we calculate % change in mass?

(final mass - intial mass)/initial mass x 100

Define 'active transport'.

Movement of particles against the concentration gradient (low to high) using energy in the form of ATP

Explain the importance of active transport in plants.

Root hair cells carry out AT to absorb mineral ions effectively in dilute soil

Explain the importance of active transport in animals.

Cells in gut lining does AT to absorb glucose effectively from the bloodstream

State one adaptations cells may have if they need to carry out active transport.

Lots of mitochondria for respiration for energy

How does active transport differ from diffusion and osmosis?

AT uses energy, D and O do not

State two differences beween diffusion and osmosis.

D: Any particles, does not need a membrane; O: Water specific, needs partially permeable membrane

State the relationship between size and surface area to volume ratio.

The bigger the size, the smaller the SA:V

Describe three adaptations of exchange surfaces.

Large SA, thin membrane/surface, ability to maintain high conc difference

How are alveoli adapted for efficient gaseous exchange?

Large SA, thin membrane (short diffusion distance), rich blood supply (maintain steep conc gradient)

How are plant roots adapted for efficient water and mineral absoprtion?

Large SA (root hairs), transpiration stream

How does stomata help maintain efficient gas exchange in leaves?

Allow gases to move in and out of leaf, maintaining steep concentration gradient

What is a gene?

A short section of DNA that codes for a protein/controls a characteristic

What are chromosomes?

Structures in the nucleus that carry genes

How many chromosomes are in one human body cell?

46

Chromosomes are arranged in ___ pairs in a human body cell.

23

How many percent of your chromosomes have you inherited from your father?

50%

Briefly describe the cell cycle.

Cell content (including DNA) is replicated, mitosis occurs to make two genetically identical cells

Define 'mitosis'.

Cell division that produces two genetically identical daughter cells

Which type of reproduction is based only on mitosis?

Asexual

State three key importances of mitosis.

Growth, repair, asexual reproduction

Briefly describe the first stage in the cell cycle.

Cell size increase, DNA and organelle replication

Briefly describe the second stage (mitosis) in the cell cycle.

Nucleus divides - One set of chromosomes is pulled to each end of the dividing cell

Briefly describe the third stage in the cell cycle.

Cytoplasm and cell membrane divides into two daughter cells

What has to happen to the cell before mitosis to ensure we can two genetically identical daughter cells?

DNA and organelles must replicate before division

Define 'differentiation'.

The process where a cell becomes specialised/adapted to perform specific functions

Define 'stem cell'.

Undifferentiated cell with the potential to become specialised

Define 'adult stem cells'.

Stem cells that can only differentiate into a specific type of cell