Cells, Respiration & Homeostasis


Eukaryotes & Prokaryotes

All cells can be classified as either EUKARYOTES or PROKARYOTES.

EUKARYOTES are plants, animals. fungi, moss and algae.

PROKARYOTES are mainly bacteria.

PLANT CELLS - tough cellulose cell walls, chloroplasts, large vaucole (cell sap), box-like shape, nucleus at the side of cell.

ANIMAL CELLS - no cellulose cell wall, no chloroplasts, sometimes small vacuole (no cell sap), shape varies, nucleus in the middle of cell.

Eukaryotes have small structures (chloroplast, nuclues etc.) which have a small membrane and each have a special function. The small membrane is called an ORGANELLE.

Prokaryotes don't have organelles.


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Specialised Cells

As cells have lots of different functions, they are often specialised to do a particular job. This means that they have special features that make them well adapted to carrying out these functions.

The specialisation of cells starts about 2 weeks after fertilisation.

Fertilisation produces a fertilised egg cell known as a zygote.

The zygote goes on to divide and become an embryo.

This embryo's cells go on to differentiate into specialised cells.

At 3 months it is a foetus.

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Mitosis makes new cells for growth and repair in all living things.

That is how you get from one cell to 50 billion.

Mitosis is also called copying division. 

Each cell can keep dividing by mitosis.

Stem cells are able (in the embryo) to differentiate into any specialised cell.

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(smallest) 1/1000 micrometer = 1 nanometer

1/1000 milimeter = 1 nanometer

(largest) 1/1000 meter = 1 milimeter

Something the size of 1 nanometer cannot be seen by the a light microscope.

Microorgansims are prokaryotes.

Optical Microscope -up to 1 micrometer

Electron Microscope -beyond 10 micrometers

A light microscope is known as an optical microscope.

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Microscopes (cont.)

An electron microscope is used to see smaller things. They use a beam of electrons instead of light rays. They show up on a fluorescent screen which can be photographed. It can magnify up to 500 000 times. We can also see inside the cell in detail.

Ribosomes and chloroplasts can only be seen with an electron microscope in detail.

magnification =       size of image

                        actual size of object

Light Microscope - light with a longer wave length, portable, see up to 500 magnification, see with eye

Electron Microscope - ray of electrons like a way, large, see great detail, a digitalised photo and colour

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Diffusion is the movement of particles from a high concentration to a lower concentration until they are spread out evenly.

Key words: concentration gradient, movement, kinetic energy

Dissolved substances have to pass through the partially permeable cell membrane to get into or out of a cell. Diffusion is one of the processes that allows this to happen.

Permeable - if something is permeable, things can get through

The molecules of food and oxygen diffuse out of the blood and into the cells.

Carbon dioxide and waste chemicals diffuse out of the cells and into the blood.

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Diffusion (cont.)

Factors which affect diffusion of substances in and out of cells:

-temperature - higher temperature, faster rate of diffusion

-diffusion concentration gradient

-thickness of any barrier between the two substances (ie. cell membrane)

In all cells molecules are diffusing across a cell membrane (7-10nm). The thickness does not vary and organsims usually have no trouble with diffusion.

Diffusion is a pasive process and does not need extra energy.

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Diffusion (cont.)

Effect of Surface Area:Volume

Multicellular organisms need specialised organs to allow all oxygen, carbon dioxide and glucose to diffuse in and out of cells.

Animals have lungs with aveoli and large surface area.

Plants have large leaves

As a cell grows its surface area/volume ration gets smaller. This means that the volume of the cell is increasing a lot faster than it's surface area.

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Photosynthesis is a chemical reaction:

carbon dioxide + water --> glucose + oxygen

It needs light energy from the sun and chlorophyll in the chloroplasts.

The glucose produced is transported through the phloem vessels to all the cells. The glucose is needed for respiration to produce energy.

If the glucose is not needed, it is chemically converted to a large molecule called starch.

Factors that limit photosynthesis are:

the amount of carbon dioxide / the temperature / the light intensity

These are all limiting factors

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Aerobic Respiration

glucose + oxygen --> carbon dioxide + water + energy

Living things need energy to stay alive. They transfer chemical energy from the food they eat. Energy is released to do work during respiration. You use this energy to keep going. 

Respiration is the release of energy from glucose into living cells. This energy release takes place all the time. The more energy needed, the faster the rate of respiration.

Hydrogen carbonate indicator turns yellow when carbon dioxide is present and purple if carbon dioxide is used up.

Fermentation is:

glucose --> alchol + carbon dioxide + energy

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There are some chemical reactions that are necessary for all the processes in living organisms.

Metabolic rate is the speed at which the reactions occur.

Examples include:

-photosynthesis (in plants)


Metabolism includes the synthesis (building up) of large molecules from small (e.g. glucose --> starch)

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Keeping conditions steady inside the body is called homeostasis.

Internal factors controlled include:

1) water concentration of the blood

2) temperature of the blood

3) glucose in blood

4) carbon dioxide produced by aerobic respiration

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Negative Feedback

Negative feedback is getitng back to the normal body temperature when the blood gets too hot or cold. The body provides negative feedback to the brain.

When the blood gets too hot, the brain switches on cooling mechanisms to cool the temperature of the blood and resume normal body temperature.

When the blood gets too cold, the brain switches on warming mechanisms to resume normal body temperature. 

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This is the maintenance if the blood temperature at 37.4*C.

Birds and mammals are the only vertebrates that can do this. These organisms are known as homiothermic. 

If the core temperature exceeds 39*C, it is called HYPERthermia.

If the core temperature is less than 33*C, it is called HYPOthermia.

The thermoregulatory centre in the hypothalamus senses the temperature of the blood flowing through the hypothalamus.

The hypothalamus also receives infomation via sensory neurones from heat receptors in the skin.

If the body core temperature starts to drop, the hypothalamus triggers responses which either reduce heat losses or produce more heat.

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Vasodilation & Vasoconstriction

Blood carries heat from the core around the body.

As blood flows through the carpilarys close to the surface of the skin, heat is lost to the body's surroundings.

The aterioles which supply the capillaries in the skin have smooth muscles in their walls. This means that the arterioles can dilate or constrict to control the flow of blood in the capillaries.

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Vasodilation is a cooling mechanism.

If the core temperature of the body starts to rise, then the smooth muscle in the arteriole walls relax and the arteriole dilates (gets wider).

More blood then flows through the capillaries near the surface of the skin.

This increases the rate of heat loss from the body.

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This is a warming mechanism.

If the core temperature of the body starts to drop, then the smooth muscles in the arteriole walls contract which constricts the arteriole.

Less blood flows through the capillaries close to the surface of the skin as blood is redirected through the shunt vessel which are found in the dermis layers of the skin.

This decreases the rate of heat loss from the body.

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The Pili Erector Muscles and Goosebumps

Each of our body hairs has a small muscle attached to its base.

When this muscle contracts, the hair is pulled upwards.

When the rate of heat loss from the body increases, these muscles contract so that the hairs stand on end, forming an insulating layer of still air. This reduces the rate of heat loss.

As the muscle contracts, we can see this in the skin as goose bumps appear.

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Sweating & Shivering

Sweating is a cooling mechanism.

As body temperature starts to increase, glands in the skin start to produce sweat. 

Water in the swear evaporates. In order to do so, it must absorb heat from the body. This increases the rate of heat loss from the body.

Shivering is a warming mechanism.

Muscles require energy to contract. This energy is supplied by respiration.

During respiration some energy is always lost as heat energy.

When we shiver, the muscles contract repeatedly so that the rate of respiration in the muscles increases, and more heat is generated.

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The Nervous System

The central nervous system is the brain and the spinal cord.

The nervous system includes the cranial system and the spinal nerves. 

The Pathway in a Reflex Action

1) A stimulus is detected by a receptor organ (e.g. retina in eye)

2) A nervous impule is sent to a coordinator (brain or spinal cord)

3) Then another impule is sent to an affector (muscle or glands)

4) This causes a response

-Nervous impules travel along the neurones (nerve cells)

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Reflex Arc

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Where two neurones meet, there is a tiny gap called a synapse.

Signals cross this gap using chemicals.

One neurone realses the chemical (a neurotransmitter) into the gap.

The chemical diffuses across the gap and makes the next neurone transmit an electrical signal.

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FMRI = functional MRI

Depressant drugs can bind with the receptor molecules in the membrane of the adjacent neurones and block the transmission of an impulse.

Stimulants can cause more neurotransmitters to cross the synapse.

Alchol is a depressant.

Caffine is a stimulant.

SSRI's are a group of anti-depressants that stop serotonin (pleasure) being destroyed.

Once the synapse is passed, the neurone transmitters are destroyed for further use. 

stimulus --> receptor -->coordinator --> effector --> response

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The Brain (diagram)


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The Brain - Cerebral Cortex

Cerebral Cortex

There are two cerebral hemispheres connected together.

The neurones which make up the cerebral cortex coordinate:

1. infomation from sensory organs

2. voluntary movements

3. our sense of self - identity

4. speech and language

5. memory and learning

6. our thoughts and intellect; design and creativity

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The Brain - The Cerebellum

This part of the brain is not under our control and works automatically.

-It is responsible for smooth cooridnated movement and muscle tone.

-Maintains our posture and balance through nervouse impulses from all our sense organs.

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The Brain - The Brain Stem

The brain stem is also called the medulla oblongata.

-Regulates our heart beat, breathing rate, blood vessel diameter and other vital impulses from other parts of the brain and spinal cord.

-Allows reflexes to be coordinated automatically.

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The Eye (diagram)

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