biology revision

Biology 4

Biology 4

Pictures.

Make a note of what pictures you see and how they are relevant to the topic.

The Basics of Homeostasis. • Homeostasis is maintaining a

constant internal environment. • The conditions in your body need

to be kept steady so that cells can function properly.

• You need to keep your water content balanced as well as your body temperature.

• Climbing to high altitudes can also affect your blood oxygen level. The higher up you are the less pressure which means less oxygen is available. This can lead to altitude sickness.

• A scuba diver’s temperature will drop in cold water. The lower down you go the higher the pressure and more oxygen is pushed into the blood. If too much oxygen is in the blood the diver could suffer from Oxygen Toxicity.

Strenuous exercise and extreme climates can effect homeostasis.

Exercise Climate.

Sweat

Heat generation

Breathing rate increases.

Salt levels decrease

(sweating)

Hot climates have the same effect as exercise.

Cold climates can cause your body temperature to decrease rapidly.

Questions.

• What is homeostasis?• What affect does high altitudes have on t

he body?• What affects does high altitudes have on

the body?• Why is homeostasis important?• How does strenuous exercise affect

homeostasis?• How does climate affect homeostasis?

Negative feedback• A mechanism called negative

feedback helps to control a constant internal environment.

• When something in your body is too low or high negative feedback gets it back to how it should be.

• Some artificial systems function like body control systems. For example incubators.

Receptor = detects the stimulus (change).

Processing Centre (brain) = receives the information and coordinates a response.

Effectors = produce the response which counteracts the change.

Some effectors work antagonistically. For example one heats and the other cools. This enables it to produce a very precise temperatures.

This mechanism allows a more sensitive response.

Questions.

1. What does negative feedback control?2. Describe how negative feedback works?3. What is a receptor?4. What is the job of a processing centre?5. What does the effectors do?6. Describe how and why some effectors

work antagonistically.

Diffusion Diffusion is the passive overall movement of particles from a region of

their higher concentration to a region of their lower concentration.

Diffusion happens in both gases and liquids.

•Some chemicals can diffuse across cell membranes. Diffusion across cell membranes are important as it’s one of the ways cells can obtain the things they need to function.

•Cells produce CO2, this mean that they will always be a higher concentration of it in the cell than In the blood.

•Dissolved food (glucose) diffuse from the blood into the cells.

Questions.

1. What is the definition of diffusion?2. Where does diffusion happen?3. Why is diffusion over a cell

membrane important?4. What do cells produce?5. What enter and leaves the cell

through diffusion of the membrane?

Osmosis • Osmosis is the overall

movement of water from a dilute to a more concentrated solution through a partially permeable membrane.

• Partially permeable means that it only allows certain substances to diffuse through it. (cell membrane).

• An animal cell can not withstand big changes in the amount of water they contain.

• If a cell has too mach water in it, it can rupture (burst). This kills the cell.

• It a cell doesn’t have enough water it will shrivel up and will not be bale to function properly.

Questions

1. What is the definition of osmosis?2. What is it a special type of?3. What is a Partially permeable

membrane?4. What can a animal cell not

withstand?5. Why would a cell rupture?6. What causes a cell to shrivel?

Enzymes • Enzymes are proteins that

speed up chemical reactions. • Enzymes are very specific. • Chemical reactions usually

involve things being split apart or joined.

• A substrate is a molecule that is changed in a reaction.

• An active site is the part of the enzyme that the substrate joins with.

• Enzymes usually only speed up a certain chemical reaction.

• Enzymes need a specific pH and temperature to work at their optimum.

• If the temperature is too great the enzyme will denature.

• Enzymes just work slower in colder conditions.

• Most enzymes work best at pH7, but not all.

Question.

1. What are enzymes?2. What do chemical reactions usually involve?3. What Is a substrate?4. What and where is an active site?5. When do enzymes work at their optimum?6. When do enzymes denature?7. What happens to enzymes in cold conditions?8. What happens to enzymes at high

temperatures?

Controlling Body Temperatures• Reactions usually work best at body temperature (37).

• The amount of heat lost must be the same as heat gained. • Receptors in the skin detect external temperatures. • The hypothalamus (part of the brain) detects the temperature of the blood.

Too hot. Too cold.

Blood vessels dilate (get bigger) (vasodilatation)

This allows more heat to escape.

The sweat gland produce more sweat to cool the body down.

Blood vessels constrict (get smaller)

(Vasoconstriction)

This allows less heat to escape.

The body shivers (muscles contract rapidly), This increases the rate of respiration and warms the tissue surrounding the muscle.

Questions

1. At what temperature do reactions usually happen at?

2. What must be the same as what?3. What and where is a

hypothalamus?4. What happens when you are too

hot?5. What happens when you are too

cold?

Heat Stroke

Symptoms.

Headaches DizzinessNausea

Vomiting Loss of appetite

ConfusionDisorientation

Visual hallucinations

Treatment

Cool the patient down

VentilationDrinks

Heat Stroke is caused by an uncontrolled increase In body temperature.

Although sweating does cool down the body down, it also makes the body become dehydrated.

Questions

• What is heat stroke?• What are the symptoms of heat

stroke?• How would you go about treating

someone with heat stroke?• How so people with heat stroke

become dehydrated?

Hypothermia

Symptoms

Shivering Low energy Confusion

Feeling fearful Loss of control of limbs

Memory loss Unconsciousness

Treatment

Warming the patient upWarm, dry clothesInsulating blankets

Hypothermia occurs when the core body temperatures falls below 35 degrees.

Questions.

1. What is Hypothermia?2. What are the symptoms of

Hypothermia?3. How would you go about treating

someone with Hypothermia?

Biology 5

DNA – Making Proteins. • All of the instructions for how to grow

and develop are contained in your DNA.

• DNA molecules contain a genetic code which is basically a long list of instructions on how to make a certain protein.

• DNA is a a double helix of paired bases.

• Each strand is made up if nucleotides and these each contain a base.

• They are 4 different bases, (A,T,C,G)• A and T are always together and so

are G and C.

• DNA controls the production of proteins in a cell.

• Proteins are made by joining amino acids together in a particular order.

• Each set of 3 bases is called a triplet. They are codes for one amino acid.

• DNA also determines which genes are switched on a off.

Proteins are made by Ribosome's.

•Proteins are made in the cytoplasm of cells, by organelles called Ribosome's.

•Because DNA is big it can not move from the nucleus of the cell.

•DNA can be copied using RNA.

•RNA is like a big messenger between the DNA and the ribosome.

Questions.

• What do DNA Molecules contain?• Describe the structure of DNA. • Name the four bases in a nucleotide. • What does DNA determine?• What are proteins made by?• Can DNA move outside the nucleus and why?• What molecule copied DNA?• Where is the ribosome located within a cell?

Cell Division – Mitosis • Your cells have to divide if your body

wants to grow., this means you DNA has to be copied.

• New cell are needed for growth and repair.

• First the cell physically grows and duplicates its contents.

• Then it splits into two by Mitosis.

21. The cell has 2 copies of it’s DNA all

spread out in long strings. 2. Before the cell divides, the DNA

forms X-shaped chromosomes. Each “arm” of the chromosomes an exact duplicate of the other.

3. The chromosomes then line up at the centre of the cells and cell fibres pull them apart. The two arms of the chromosome go to opposite ends of the cells.

4. Membranes form around each of the sets of chromosomes these become the nuclei of the two new cells.

5. Lastly the cytoplasm divides.

1

The cell has to copy everything it contains so that when it splits both

cell have the same content.

The number of organelles increases during cell growth.

The chromosomes are, so that the cell has two copies of it’s DNA.

Questions.

1. Why are new cells needed?

2. What is the first step of cell division?

3. Describe the process of mitosis.

Cell Division – Meiosis.

Cell divide by meiosis to form sperm or egg cells. (gametes)

Gametes have half the usual number of chromosomes.

When a sperm and egg cell join together they form a zygote.

Meiosis involves two divisions and produced four daughter cells.

Meiosis.

1. The DNA duplicates. On arm of the chromosome id identical to the other.

2. In the first division the chromosome pairs line up in the centre of the cell.

3. The pairs are then pulled apart.

4. In the final division the chromosomes line up again and then it splits again.

Questions.

• What does Meiosis make?

• How many daughter cells does it produce?

• How many divisions does it make?

• Describe the process of Meiosis.

Development from a single cell.

• Cells in an early embryo can turn into any type of cell. (embryonic stem cells).

• In humans all the cells in and embryo are undifferentiated up until the eight cell stage.

• The process of the cells becoming specialized is called differentiation.

• All cells contain the same genes but not all are turned on.

• Adult humans only have stem cells in certain places like bone marrow. These can only turn into some cells unlike embryonic stem cells.

Stem Cells.

Stem cells may be able to cure many diseases.

Adult stem cells are already used to cure diseases. For example people with some blood diseases can be treated by bone marrow transplants.

Embryonic stem cells can be extracted from very early human embryos.

Cloning could also be used to make Stem cells.

Questions

• What is an embryonic stem cell?

• Do adult cells have stem cells?What could stem cells be used for?

• What is a zygote?

• What could cloning produce?

Growth in Plants • Plants can regenerate and grow almost

continually all through their life.

• Animals stop growing but plants do not.

• Even really old trees will keep putting out new branches.

• Plants grow in height due to cell enlargement.

• Meristems are plant tissue, they contain unspecialised cell , these enable them to form any type of cell.

• If hormone conditions are correct the unspecialised cells can turn into plant tissue or organs.

• Cells contain all the same DNA and its just a matter of which genes are on and which are off.

• Meristems are found in roots and shoots.

Clones can be produced from cuttings.

Cuttings contain unspecialised meristem cells which can differentiate to make any cell.

This means a whole new plant can grow from a cutting.

Questions.

• What do plants do that animals can’t?

• What causes plants to grow?

• What are meristems and where are they found?

• What can cuttings be turned into?

Phototropism and Auxins.

Phototropism.

• Phototropism is movement in response to light.• Shoots grow towards the light and roots away. • Photosynthesis occurs mainly in the leaves so

they grow towards the lights.

• Auxins are plant growth hormones. • Auxins are chemicals that control growth

near the tips of shoots and roots. It enlarges the cells.

• If the tip of the shoot is removed no Auxins can be made.

• Auxins make the shoot grow towards the light.

• Auxins hide in the shade.

Auxins help cuttings grow Into full plants.

If you just stick a cutting in soil it wont always grow. If you add rooting powder it makes a

good result more likely. Rooting powder contains Auxins. This helps produce clones in

the easiest way.

Questions.

• What is phototropism?

• What are Auxins?

• Where do Auxins hide?

• What do Auxins help grow?

• What is in rooting powder?

Biology 6

The Nervous System

The Nervous System

Reflexes

Learning and modifying reflexes.

Brain development and learning

Learning skills and behaviour.

Studying the Brain