Biology topic 1

Question 1

What is a prokaryote?

Answer 1

A prokaryotic cell is also known as a prokaryote, it’s a single celled organism, smaller, and simpler than both eukaryotic, animal, and plant cells.

Question 2

What is a eukaryote?

Answer 2

Eukaryotes are organisms made up of eukaryotic cells, they are complex and include all animal and plant cells.

Question 3

What does a animal cell contain?

Answer 3

A nucleus (contains genetic material, and controls the cells activities).
cytoplasm (gel like substance, where most chemical reactions happen)
Cell membrane (barrier, controls what enters the cell)
Mitochondria (aerobic respiration happens here)
Ribosomes (where proteins are made in the cell)

Question 4

What are the different parts of a cell called?

Answer 4

Sub cellular structures

Question 5

What does a plant cell contain?

Answer 5

Everything that an animal contains, but also three more things.
Rigid cell wall - made of cellulose, strengthening the cell.
Permanent vacuole - contains cell sap, a week solution of sugar and salt.
Chloroplasts - where photosynthesis takes place, contains a green substance, called chlorophyll, which absorbs the light needed for photosynthesis.

Question 6

What is a bacteria cell and what does it contain?

Answer 6

A bacteria cell is a prokaryote, containing;
Cytoplasm
Cell membrane
Cell wall
Single strand of DNA, floating freely in cytoplasm
Small rings of DNA called plasmids.

Question 7

What is a microscope?

Answer 7

Microscopes, let us see things we can’t see with the naked eye. As technology and knowledge have improved, microscopy techniques, have developed.

Question 8

What is a light microscope?

Answer 8

Uses light and lenses to form an image of a specimen and magnify it, letting us see individual cells and large sub cellular structures like nuclei.

Question 9

What is an electron microscope?

Answer 9

Using electrons, instead of light to form an image, they have a much higher magnification than light microscopes. They have a higher resolution, giving a sharper image. They let us see much smaller things in more detail, like the internal structure of mitochondria and chloroplasts.

Question 10

What is the formula for magnification?

Answer 10

Magnification = image size divided by real size

Question 11

How does standard form work? Give an example

Answer 11

E.g 2.5 x 10 (to the power of -3) = 0.0025
3 x 10 (to the power of 5) = 300, 000

Question 12

How do you prepare your slide to put under the microscope?

Answer 12

1) add a drop of water to the middle of a clean slide.
2) cut up and onion and separate it out into layers. Use tweezers to peel off some epidermal tissue from the bottom of one of the layers.
3) using tweezers, place the epidermal tissue into the water on the slide.
4) add a drop of iodine solution (stain), highlighting objects in a cell.
5) place a cover slip (thin sheet of glass/plastic), on top, carefully tilt and lower it with the tweezers, so it covers the specimen, try not to get any air bubbles as they will obstruct the view of the specimen.

Question 13

How do you use a light microscope?

Answer 13

1) clip the slide you’ve prepared onto the stage.
2) select the lowest powered objective lens.
3) use the course, adjustment knob to move the stage up to just below the objective lens.
4) look down the eyepiece, use the coarse adjustment knob to move the stage downward till the image is roughly in focus.
5) adjust the focus with the fine adjustment knob until you get a clear image.
6) if you need to see with greater magnification, swap to a high-powered objective lens then refocus.

Question 14

How do you draw observations?

Answer 14

Use a pencil with a sharp point.
Needs to take up, at least half of the space, clear, unbroken lines.
No colouring or shading.
Subcellular structures should be drawn in proportion within cells.
Include a title of what you were observing, and the magnification.
Label important features using straight and uncrossed lines.

Question 15

Why do cells differentiate?

Answer 15

To become specialised

Question 16

What is differentiation?

Answer 16

When cells change to become specialised, different subcellular structures, turn into different types of cell to carry out different functions.
Most differentiation occurs as an organism develops, in most animal cells ability to differentiate is lost at an early stage after they become specialised.
The cells, the differentiate immature animals are mainly used for repairing and replacing cells, such as skin or blood.
undifferentiated cells are called stem cells.

Question 17

List the five types of specialised cell , you need to know?

Answer 17

Sperm, nerve, muscle, root hair, phloem, and xylem.

Question 18

What is a sperm cell?

Answer 18

Specialised for reproduction, function is to get the mail DNA to the female DNA. Long-tail and streamline head to help it swim. Lots of mitochondria to provide the cell with energy. Carries enzymes in its head to digest through the egg cell membrane.

Question 19

What is a nerve cell?

Answer 19

Specialised for rapid signalling, function is to carry electrical signals from one part of the body to another. Hence, the cells along to cover more distance, and have branched connections at their ends, to connect to the other nerve cells and form a network throughout the body.

Question 20

What is a muscle cell?

Answer 20

Specialise for contractions, they are long so they have space to contract and contain lots of mitochondria to generate energy.

Question 21

What is a root hair cell?

Answer 21

Specialised for absorbing water and minerals, found on the surface of plant roots, 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.

Question 22

What are phloem xylem cells?

Answer 22

Specialised for transporting substances.
They can both form tubes which transports substances such as food and water around plants. To full knees, the cells are long, and joined to end to end. Xylem cells are hollow in the centre. Phloem cells have very few sub cellular structures, so that stuff can flow through them.

Question 23

What is a chromosome?

Answer 23

Chromosomes contain genetic information.
Most cells contain a nucleus containing DNA in the form of chromosomes.
They are coiled up lengths of DNA molecules.
Each one carries a large number of genes, each controlling different characteristics.
Body cells, usually have two copies of each chromosome, one from mother, and one from father.
Usually, each human cell contains 23 pairs of chromosomes.

Question 24

What is the cell cycle?

Answer 24

Body cells in multicellular organisms divide to produce new cells as a part of series of stages, called the cell cycle.
The stage in this cycle when the cell divides is called mitosis.
Multicellular organisms use mitosis to grow or replace cells that have been damaged.
The end of the cell cycle results in two new cells identical to the original one with the same number of chromosomes.

Question 25

What is growth and DNA replication?

Answer 25

In a cell, that’s not dividing DNA is spread out in Long strings. Before dividing it has to grow an increase the amount of sub cellular structures such as mitochondria. It then duplicates its DNA, so there’s 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.

Question 26

What is mitosis?

Answer 26

The chromosomes lineup at the centre of the cell, and cell fibres pull them apart. The two arms of each chromosome go to the opposite ends of the cell. Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells (the nucleus has divided). Lastly, the cytoplasm and cell membrane divide. This means the cell has now produced two new daughter cells containing the exact same DNA. They are identical to each other and the parent cell.

Question 27

What are embryonic stem cells and what they do?

Answer 27

Differentiation is when a cell changes to become specialised. Undifferentiated cells (stem cells), can divide to produce lots more of themselves, and different types of cell. Stem cells are usually found in early human embryos. They have potential to turn into any kind of cell at all. (This makes sense because different types of cells found in a human being have to come from those few cells in the early embryo). Adults also have stem cells, but they’re only found in specific places. E.g. bone marrow. They can only turn into specific types of cells. E.g. blood cells. Stem cells are made from embryos and bone marrow can be grown in a lab to produce clones, and made to differentiate into specialised cells to use in medicine etc.

Question 28

How can stem cells cure many diseases?

Answer 28

This is already been proven with adult stem cells, curing disease, by being transferred from the bone marrow of a healthy person replacing faulty blood cells in someone else. Embryonic stem cells could also be used to replace faulty cells, such as insulin producing cells for people with diabetes. In therapeutic cloning, an embryo could be made to have the same genetic information as the patient, meaning stem cells produced from, it would also contain the same genes, and wouldn’t be rejected.

Question 29

What are the risks of using stem cells in medicine?

Answer 29

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

Question 30

Why are some people against stem cell research?

Answer 30

Some people believe that human embryo shouldn’t be used for experiments since each one is a potential human life. Others think the curing existing patients who are suffering is more important. Phone convincing argument in favour is that the embryos used in the research are usually unwanted ones from fertility clinics, which would’ve been destroyed anyway. These campaigners feel scientist to concentrate more on finding in developing other sorts of stem cells, so people could be helped without having to use embryos. In some countries stem cell research is banned.

Question 31

How can stem cells produce identical plants?

Answer 31

In plants stem cells are found in the meristems. Throughout a plant life cells in the meristem tissue is can differentiate. The stem cells can produce clones of whole plants quickly and cheaply. These can be used to grow more plants of a species. Stem cells can also be used to grow crops of identical plants that have desired features for farmers e.g. disease resistance.

Question 32

What is diffusion?

Answer 32

Diffusion is the spreading out of particles from an area of high concentration to an area of lower concentration. Diffusion happens in solutions and gases, as particles are free to move about randomly. The simplest type is when different gases diffuse through each other e.g. perfume. The bigger, the concentration gradient, the faster the diffusion rate. A higher temperature will also give a faster diffusion rate because the particles have more energy to move faster.

Question 33

Cell membranes and diffusion

Answer 33

Cell membranes are known as a barrier, controlling what comes in and out of the cell. Dissolves substances can move in and out by diffusion. Only very small molecules can does fuse through cell membranes eg. Oxygen, glucose, water. Big molecules like starch and proteins can’t fit through the membrane. Just like with diffusion in air, particles flow through the cell membrane from where there is a higher concentration to a lower concentration. They move randomly, if there are lots of particles on one side, there is an overall net movement. The larger, the surface area of the membrane, the first of the diffusion rate, because more particles can pass through at once.

Question 34

What is osmosis?

Answer 34

Osmosis is the movement of water particles across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration. It’s a type of diffusion.

Question 35

Describe the process of osmosis

Answer 35

Partially permeable membrane means it has very small holes in it, so only tiny molecules can pass through it. The water molecules pass both ways through the membrane during osmosis. This happens because water molecules move about randomly. Because there are more water molecules on one side than the other there is a steady net flow of water into the region of fewer water molecules. (Stronger sugar solution) This means the strong sugar solution gets even more dilute. The water acts like it’s trying to even up the concentration either side of the membrane.

Question 36

What is the practical you can do to observe the effect of sugar solutions on plant tissue?

Answer 36

The potato experiment, you cut a potato, place one cylinder into a beaker full of 20cm3 water. Do exactly the same for the other beaker, but add sugar. At the end of this experiment, you will need to weigh each potato, and if they have increased in mass, then they have drawn in water by osmosis.

Question 37

What is active transport?

Answer 37

The process of substances needing to be absorbed against a concentration gradient, e.g. from a lower to a higher concentration

Question 38

Why do root hair cells take in minerals and water?

Answer 38

Each branch of a root will be covered in millions of microscopic hairs. This gives the plant a large surface area for absorbing water and mineral ions from the soil. Plants need this mineral ions for healthy growth. The concentration of minerals is usually higher in the root hair cell than in the soil around them. The root hair cells can’t use diffusion to take up minerals from the soil.

Question 39

How do you root hair cells use active transport to take in minerals?

Answer 39

Minerals should move out of the root hairs if they followed the rules of diffusion. The cells must use another method to draw them in. The method is active transport. This process allows the plant absorb minerals from a very dilute solution against a concentration gradient. This is essential for its growth. But active transport needs energy from respiration to make it work. Active transport also happens in humans for example in taking glucose from the gut and from kidney tubules.

Question 40

Why is active transport crucial to stop us starving?

Answer 40

Active transport is used in the gut where there is a lower concentration of nutrients in the gut, but a higher concentration of nutrients in the blood. When there’s a higher concentration of glucose and amino acids in the gut, the diffuse naturally into the blood. But, sometimes there’s a lower concentration of nutrients in the gut than there is in the blood. This means that the concentration gradient is the wrong way. Active transport allows nutrients to be taken into the blood, despite the fact that the concentration gradient is the wrong way. This means the glucose can be taken into the bloodstream when its concentration in the blood is already higher than in the gut. At this point, it can then be transported to the cells where it’s used for respiration.

Question 41

How do organisms exchanges substances with their environment?

Answer 41

Cells can use diffusion to take in substances they need and get rid of waste products. For example, oxygen and carbon dioxide are transferred between cells and the environment during gas exchange. In humans, urea defuses from cells into the blood plasma for removal from the body by the kidneys. How easy it is for an organism to exchange substances with its environment depends on the organism surface area to volume ratio.

Question 42

How can you compare surface area to volume ratios?

Answer 42

A ratio shows how big one value is compared to another. The larger an organism is, the smaller it surface area is compared to its volume. You can you show this by calculating surface area to volume ratios.

Question 43

Why do multicellular organisms need exchange surfaces?

Answer 43

single celled organisms, gases and dissolved substances can diffuse directly in or out of the cell across the cell membrane. Due to a large surface area compared to volume - enough substances can be exchanged across the membrane to supply the volume of the cell. Multicellular organisms have a smaller surface area compared to volume - not enough substances can diffuse from their outside surface to supply their entire volume. Meaning they need some sort of exchange surface for efficient diffusion. The exchange surface structures have to allow enough of the necessary substances to pass through.

Question 44

How have exchange surfaces adapted to maximise effectiveness?

Answer 44

Thin membrane - substances only have a short distance to diffuse. Large surface area - lots of substance, can diffuse at once. Exchange surfaces, an animals have lots of blood vessels to get stuff into an out of the blood quickly. Gas exchange surfaces in animals e.g. alveoli, often ventilated to - air moves in and out.

Question 45

What happens with gas exchange in the lungs?

Answer 45

The job of the lungs is the transfer oxygen to the blood, and to remove waste carbon dioxide from it. To do this, the lungs contain millions of little SX called alveoli, where gas exchange takes place. The alveoli are specialised to maximise the diffusion of oxygen and carbon dioxide. They have; An enormous surface area a moist lining for dissolving gases Very thin walls A good blood supply

Question 46

How did the villi provide a really big surface area?

Answer 46

The inside of the small intestine is covered in millions and millions of tiny little projections called villi. They increase the surface area in a big way, so that digested food is absorbed, much more quickly into the blood. They have a single layer of surface cells, and a very good blood supply to assist quick absorption.

Question 47

How does the structure of leaves let gases diffuse in and out of cells?

Answer 47

Carbon dioxide diffuses into the air spaces within the leaf, then into the cells where photosynthesis happens. (Adapted structure) The underneath of the leaf is an exchange surface covered in holes called stomata, we are carbon dioxide diffuses in through. Oxygen and water vapour diffuse out through the stomata. The size of the stomata are controlled by Guard cells, which close them if the plant is losing water faster than it is being replaced by the roots. (Without these the plant with soon wilt). The flat in shape of the leaf increases the area of this exchange surface to make it more effective. The walls of the cells inside to leave form another exchange surface, the air spaces inside the leaf, increase the area of this, so there’s more chance for carbon dioxide to get in. The water vapour evaporates from the cells inside the leaf. Then it escapes by diffusion, because there is a lot of it inside the leaf and less of it in the air outside.

Question 48

How do you gills have a large surface area for gas exchange?

Answer 48

Water (containing oxygen) enters the fish through the mouth and passes out the gills. As this happens, oxygen diffuses from the water into the blood in the gills and carbon dioxide diffuses from the blood into the water. Each Gill is made of thin plates, called gill filaments, which give a big surface area for exchange of gases. The Gill filaments are covered in lots of tiny structures called lamellae, increasing the surface area. The lamellae have lots of blood capillaries to speed up diffusion. They also have a thin surface layer of cells to minimise the distance that the gases have to diffuse. Blood flows through the lamellae in One Direction and water flows in the opposite. This maintains a large concentration gradient between the water and blood. The concentration of oxygen in the water is always higher than that in the blood, so as much oxygen as possible diffuses from the water into the blood.