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AQA GCSE Biology > Cell Biology > Flashcards

Flashcards in Cell Biology Deck (100):

What are the two types of Cells?

-Prokaryotic cells (simpler and smaller e.g. bacteria). A prokaryote is a single celled organism made up of a prokaryotic cell.
-Eukaryotic cells (complex e.g. animal and plant cells). A Eukaryote is an organism made up of Eukaryotic cells


What subcellular structures (parts of a cell) do most animal cells have?

-Cell Membrane


What is the Nucleus?

The nucleus is the part of a cell which contains genetic material that controls the activities of the cell.


What is the Cytoplasm?

The cytoplasm is a gel-like substance where most of the chemical reactions happen in a cell. It contains enzymes that control those chemical reactions.


What is the Cell Membrane?

The cell membrane holds the cell together and controls what goes in and out of the cell.


What is the Mitochondria?

The mitochondria is where most the reactions for aerobic respiration take place. Respiration transfers energy that a cell needs to work.


What are Ribosomes?

Ribosomes are where proteins are made in the cell.


What extra subcellular structures do plant cells have?

-Cell Wall
-Permanent Vacuole


What is a Cell Wall?

The cell wall is made of cellulose. It supports the cell and strengthens it.


What is a permanent vacuole?

A permanent vacuole contains sap which is a weak solution of sugar and salts.


What are Chloroplasts?

Chloroplasts are where photosynthesis occurs to make food for the plant. Chloroplasts contain a green substance called chlorophyll, which absorbs the light needed for photosynthesis.


What are the differences and similarities in a bacteria cell (prokaryote)?

-It doesn't have a "true nucleus"
-Instead it has a single circular strand of DNA that floats in the cytoplasm
-There is a cell membrane, cytoplasm and cell wall
-Bacteria doesn't have chloroplasts or mitochondria
-There may also contain one or more small rings of DNA called Plasmids


What are light microscopes?

Light microscopes use light and lenses to form an image of a specimen and magnify it. They let us see individual cells and large subcellular structures like nuclei.


What are electron microscopes?

Electron microscopes use electrons instead of light to form an image. The have a higher magnification than light microscopes and a higher resolution (sharper image). They allow us to see much smaller things in detail such as the internal structures of mitochondria and chloroplasts and even let us see ribosomes and plasmids.


What is the formula for calculating magnification of an image?

magnification = image size/real size


What are the scaling prefixes and their value?

- tera (T) = 10 to the power of 12
- giga (G) = 10 to the power of 9
- mega (M) = 1,000,000 (10 to the power of 6)
- kilo (k) = 1000 (10 to the power of 3)
- deci (d) = 0.1 (10 to the power of -1)
- centi (c) = 0.01 (10 to the power of -2)
- milli (m) = 0.001 (10 to the power of -3)
- micro (µ) = 0.000001 (10 to the power of -9)
- nano(n) = 10 to the power of -9


How do you prepare a slide?

1) Add a drop of water to the middle of a clean slide (strip of clear glass or plastic)
2) Place specimen in the centre of the slide
3) Add a stain to the specimen so the objects in the cell are highlighted with colour (iodine is a stain)
4) Place a cover slip (a square of thin, transparent plastic or glass)


What are the parts of a light microscope an what do they do?

-Eyepiece (used to look through at the formed image)
-Objective lenses (lenses that magnify the specimen with different amounts of magnification)
-Coarse Adjustent Knob (Used to lower and raise the stage)
-Stage (A platform on which the slide goes on)
-Fine adjustment knob (Used to focus the image)
-Light (used to form an image of the specimen)


What is differentiation?

Differentiation is the process in which a cell changes to become specialised for its job. The cell develops different subcellular structures to turn into different types of cells so they can carry out specific functions.


When does differentiation occur?

Most differentiation occurs as an organism develops. In many animal cells, the ability to differentiate is lost at an early stage after they become specialised. However, lots of plants cells don't lose this ability.


What cells differentiate in mature animals?

The cells that differentiate in mature animals are mainly used for repairing and replacing cells, such as skin and blood cells.


What are cells that don't differentiate called?

Some cells are undifferentiated cells and they are called Stem Cells.


How are sperm cells specialised for reproduction?

-It has a long tail and streamlined head to help it swim to the egg
-There are lots of mitochondria in the cell to provide the energy needed
-It carries enzymes in its head to digest through the the egg cell membrane
-Their job is to get the male DNA to the female DNA


How are nerve cells specialised for rapid signalling?

-The cells are long to cover more distance
-They have branched connections at their ends to connect to other nerve cells and form a network throughout the body
- Their role is to carry small electrical signals from one part of the body to another


How are muscle cells specialised for contraction?

-Cells are long so they have space to contract
-They contain lots of mitochondria to generate the energy needed for contraction
-Their job is to contract quickly


How are root hair cells specialised for absorbing water and minerals?

-Root hair cells are cells on the surface of plant roots which grow into long "hairs" that stick out into the soil
-This gives the plant a large surface area for absorbing water and minerals from the soil


How are Phyloem and Xylem cells specialised for transporting substances?

-These cells 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


Most cells in your body have a nucleus. What does a nucleus contain and how?

The nucleus contains your genetic material in the form of chromosomes.


What are chromosomes?

Chromosomes are coiled up lengths of DNA molecules. Each chromosome carries a large number of genes. Different genes control the development of different characteristics.


How many copies of chromosomes do we have?

Body cells usually have two copies of each chromosome-one from the organism's "mother" and one from its "father"


What is the cell cycle?

Body cells in multicellular organisms divide to produce new cells as part of a series of stages called the cell cycle. The part where the cell splits is called mitosis.


What is mitosis used for?

Multicellular organisms use mitosis to grow or replace cells that have been damaged.


What is the result of the cell cycle?

The cell cycle results in two new cells identical to the original cell with the same number of chromosomes.


What are the two main stages in the cell cycle?

-Growth and DNA Replication


What is the Growth and Replication stage in the cell cycle?

1) The DNA is spread out in long strings in a cell that's not dividing
2) Before it divides, the cell has to grow and increase the amount of subcellular structures such as mitochondria and ribosomes
3)The cell then duplicates its DNA so there is one copy for each new cell. The DNA is copied and forms X-shaped chromosomes. Each "arm" of the chromosome is an exact duplicate of the other.


What is the Mitosis stage of the cell cycle?

4) The chromosomes line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite "poles" (ends) of the cell.
5) Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells-the nucleus has divided
6)The cytoplasm and cell membrane divide


How do Prokaryotic cells replicate?

Using binary fission


What is the binary fission process?

1) The circular DNA and plasmid(s) replicate
2)The cell gets bigger and the circular DNA strands move to opposite poles (ends) of the cell
3)The cytoplasm begins to divide and the new cell walls begin to form
4)The cytoplasm divides and two daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have a variable number of copies of plasmids


How can bacteria divide quickly?

If they are in the right environment (e.g. a warm environment and lots of nutrients). Some bacteria such as E.Coli can take as little as 20 minutes in the right environment. If conditions become unfavourable, the cells will stop dividing and eventually begin to die.


What is an inoculating loop used for when culturing micro organisms on a culture medium?

Inoculating loops are wire loops that can be used to transfer microorganisms to the culture medium


What can be used instead of an inoculating loop?

A sterile dripping pipette and spreader for a more even cover of bacteria


What do culture mediums contain?

They contain the carbohydrates, minerals, proteins and vitamins bacteria and other microorganisms need to grow on them


Name two examples of culture mediums:

-Nutrient broth solution
-Solid agar jelly


How do you make an agar plate?

Pour hot agar jelly into a Petri dish (shallow round plastic dish)


How can you test the action of antibiotics or antiseptics on a culture of bacteria?

Place paper discs soaked in different types or concentrations of antibiotics/septics on an agar plate that has an even covering of bacteria


How will the bacteria react to antibiotics or antiseptics?

Antibiotic resistant bacteria will continue to grow but no resistant strains will die. A clear area will be left where the bacteria has died


What is the area where the bacteria has died called?

The inhibition zone (bigger the zone=better the antibiotic)


What is the control in the agar experiment ?

The paper disc that has only been soaked in sterile water so that you can see if the paper isn't weird and the difference antibiotics has


What is important about the equipment during the agar experiment?

It is sterilised before hand


Before leaving the Petri dish for 4 hours at 25 degrees Celsius, how should it be stored?

It should be stored upside down to prevent drips of condensation falling on the agar. The lid of the Petri dish should be lightly taped on to stop microorganisms from the air getting in


What are stem cells?

Stem cells are undifferentiated cells. They can divide to produce lots more undifferentiated cells.


What is the most amazing thing about stem cells?

They can turn into different types of cell depending on their instructions


Where are stem cells found?

They are found in early human embryos. Adults have stem cells but they are only in certain places like bone marrow and can only turn into certain cells not any like in an embryo.


How can stem cells be used by scientists and doctors?

The can be grown in a lab to produce clones (genetically identical cells) and made to differentiate into specialised cells for medicine or research.


How can stem cells from a healthy adult's bone marrow help?

The can be placed in a patient who needs faulty blood cells replaced.


What are two ways embryonic stem cells can be specialised to help people?

They could be made into insulin producing cells for people with diabetes or nerve cells for patients with paralysed spinal injuries.


What is therapeutic cloning and how is it useful?

In therapeutic cloning an embryo can be made to have the same genetic information as a patient. This means the stem cells would contain the same genes as the patient so would have no chance of being rejected by the body.


What are dangers with using stem cells for medicinal purposes?

Stem cells grown in a lab could become contaminated with a virus and would be passed on to a patient which could make them sicker


Where are stem cells found in plants?

The meristems


How are these stem cells used?

The are cloned to produce identical copies of whole plants quickly and cheaply. This can grow more plants of rare species or grow crops of identical plants that have desired features


What is diffusion?

Diffusion is the spreading out of particles from an are of higher concentration to an area of lower concentration


In what states can diffusion occur?

Liquids/solutions and gases


How is the rate of diffusion increased?

-with a bigger concentration gradient (difference in concentration)
-in a higher temperature (particles have more energy to move faster)
-with a larger surface area to volume ratio


How do small molecules pass through a cell?

They diffuse through the cell membrane


How is the rate of diffusion through a cell membrane increased?

The larger the surface area of a membrane the faster the diffusion rate (more particles can pass through at once)


What is osmosis?

The net movement of water from an area of higher water concentration to an area of lower water concentration through a partially permeable membrane. It is also the net movement of water from an area of low solute concentration to an area of high solute concentration.


What is a partially permeable membrane?

A membrane with very small holes. Only tiny molecules like water can pass through them.


How do the water molecules move through the partially permeable membrane?

They pass both ways through because water molecules move about randomly.


What happens to the region with fewer water molecules (the side of the membrane with fewer water molecules)?

There is a steady net flow of water into the region with fewer water molecules. The water tries to "even up" the concentration of water molecules either side of the membrane


What is osmosis a type of?

Diffusion- passive movement of water particles from a higher


How can osmosis be shown through an experiment?

1) Cut up innocent potatoes into identical cylinders
2) Get some identical beakers and put different concentrations of sugar solution and water in them
3)measure the mass of the cylinders and put on win each beaker and leave for 24 hours or so
4)after the time, take out the cylinders and dry them. Then weigh them: If water has been drawn in, their mass will increase. If water has been drawn out, their mass will have decreased


What are the different variables in the osmosis experiment?

- Dependent = Chip mass
- Independent = Concentration of sugar solution and water
- Control variables = volume of solution, temperature, time, type of sugar used etc.


What is active transport?

The process in which substances are absorbed but are going against the concentration gradient (e.g. smaller concentration into larger concentration). It does not follow the rules of diffusion. It requires energy and is therefore active


Name two places where active transport takes place:

-Root hair cells (allows plant to absorb minerals from a very dilute concentration in the soil against the concentration gradient in the root hair cell)
-The Gut (sometimes there is a lower concentration of nutrients in the gut than there is in the blood but the nutrients still need to get into the blood to be transported around the body)


What do we need to know when working out how easily stuff moves between an organism and its environment?

The surface area to volume ratio (SA:V)


What would the SA:V ratio of a large organism be like?

The larger the organism, the smaller the surface area is compared to its volume.


What is good about diffusion in single-celled organisms?

Gases and dissolved substances can be directly diffused in or out of the cell across the cell membrane. This is because they have a large surface area compared to their volume so enough substances can be exchanged across the membrane to supply the volume of the cell.


What is the problem with multi-cellular organisms and diffusion?

Multi-cellular organisms have a smaller surface area compared to their volume. This means not enough substances can diffuse from their outside surface to supply their entire volume.


What do multi-cellular organisms need for efficient diffusion?

An exchange surface


How are exchange surfaces adapted to maximise effectiveness?

-They have a thin membrane, so substances only have a short distance to diffuse
-They have a large surface area so lots of substance can diffuse at once
-Exchange surfaces in animals have lots of blood vessels, to get stuff into and out the blood quickly
-Gas exchange surfaces in animals are often ventilated


How are alveoli specialised for the diffusion of oxygen and carbon dioxide in the lungs?

-They have an enormous surface area (about 75m^2 in humans)
-They have a moist lining for diffusing gases
-Very thin walls
-A good blood supply


Where is villi located?

Millions and millions of them cover the inside of the small intestine. Their job is to absorb the digested food and nutrients into the blood using diffusion


Why is villi so good at diffusion?

-They have a single layer of surface cells
-They have a very good blood supply to assist quick absorption


Where is the exchange surface on a leaf and what parts of the leaf are found there?

It is found on the underside of the leaf. It is covered in tiny biddy holes called stomata which are controlled by guard cells. Guard cells close the stomata if the plant is losing water faster than it is being replaced by the roots.


What diffuses through the stomata?

Carbon dioxide which then diffuses into the cells where photosythesis happens. Oxygen and water vapour also diffuse out the stomata because there is more of it inside the leaf than there is outside the leaf.


Why is the leaf's exchange surface successful?

-The flattened shape of the leaf increases the surface area of the exchange surface
-The walls of the cells inside the leaf form another exchange surface. The air spaces inside the leaf increase the the area of the surface so there is more chance for carbon dioxide to get into the cells.


Where is the gas exchange in a fish?

The gills


What do the gills in a fish do?

Water enters through the fish's mouth and passes through the gills. The gills allow the oxygen to diffuse from the water into the blood. Carbon dioxide diffuses from the blood into the water


What are each gill made up of?

Gill filaments. They provide a big surface area for gas exchange.


What are gill filaments covered in?

They are covered in lots of tiny structures called lamellae which increase the surface area even more


What other characteristics of lamellae help with diffusion?

-They have lots of blood capillaries to speed up diffusion
-They have a thin surface layer of cells to minimise the distance that the gases have to diffuse


Which way does the blood and water flow in lamellae and why?

Blood flows one way through the lamellae and water flows in the opposite direction. This maintains a large concentration gradient between the water and the blood. The concentration of the oxygen in the water will always be higher than the that in the blood so as much oxygen as possible diffuses from the water into the blood


What happens to a plant cell when water moves in ?

The cell swells up and becomes turgid


What happens when water moves out of a plant cell?

The cell becomes flaccid and plasmolysis occurs


What is plasmolysis?

When the cell membrane pulls from the cell wall


What happens in an animal cell when water moves in?

The cell bursts as there is no cell wall. This is known as lysis


What happens when water moves out an animal cell?

The cell becomes shrivelled


What does isotonic mean?

Isotonic is a state in osmosis when the concentration of the solution is the same as in the cell


What does hypertonic mean?

Hypertonic is a state in osmosis where the concentration of the solution is higher than in that of the cell


What does hypotonic mean?

Hypotonic is a state in osmosis where the concentration of the solution is lower than the concentration in the cell