Combined science: Biology-B1

  • Created by: Sumaiya
  • Created on: 07-05-18 17:13

Biology-B1: Cells

Cells can either be eukaryotic or prokaryotic.

Eukaryotic: complex cells

Prokaryotic: Single cell organism

An animal cell contains:

  • Nucleus: Contains genetic materials
  • Cell Membrane: Holds the cell together+controls what goes in and out
  • Cytoplasm: Where chemical reactions happen
  • Ribosome: Where proteins are made
  • Mitochondria: Where areobic respiration happens

Plant cell contains the same things as animal cells but also contains:

  • Cell wall: Made of cellulose+supports and strenthens the cell
  • Chloroplast: Contains green substance(chlorophyll)+where photosynthesis occurs
  • Vacuole: Contains cell sap
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Biology-B1: Differentiation

Differentiation: Process by which a cell changes to become specialised for its job.

Most differentiation happens when an organism develops. Cells that differentiate in mature animals are usually for repairing and replacing cells.

Examples of specialised cells:

  • Sperm cell: Specialised for reproduction + Tail and streamlined head to help it swim + lots of mitrochondia for energy.
  • Nerve cell: Specialised for rapid signaling + Long cells to cover mor distance and have branched connections.
  • Muscle cells: Specialised for contractions + Long cells for space + lots of mitrochondria for energy.
  • Root hair cells: Specialised for absorbing water and minerals + Large surface area to absorb water and minerals from the soil.
  • Xylem and Phloem cells: Specialised for transporting substances.
  • Xylem: Hollow so stuff can flow through them.
  • Phloem: Have a few subcellular structures so stuff can flow through them.
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Biology-B1: Chromosomes

Most cells contain a nucleus.

Nucleus contain chromosomes.

Chromosomes: Coiled up lengths of DNA molecules,

Each chromosomes carries a large number of genes.

Genes: A unit of heriaty which is transferred from the parent of the offspring.

Different genes control the development of different charecteristics. E.G: Hair colour.

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

A human cell has 23 pairs of chromosomes.

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Biology-B1: Stem Cells

Undifferntiated cells are called stem cells.

There are two types of stem cells:Embryonic stem cells & Adult stem cells:

  • Embryonic stem cells: found in early human embryos + can turn into any type of cell
  • Adult stem cells: found in the bone marrow + only able to turn into certain cells

Adult stem cells are already used to cure diseases.

For example: Adult stem cells can replace faulty red blood cells in a patient.

Embryonic stem cells can be used to replace faulty cells.

For example: Embryonic stem cells can turn into insulin-producing cells for people with diabetes.

Most people are against embryonic stem cells as it could be a potential human life.

In plant cells, stem cells are found in the meristem.

Meristem: Part of the plant where growth occurs + can turn into any type of plant cells.

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Biology-B1: Diffusion

Diffusion happens both in both solutions and gases.

Diffusion: The spreading out of particles from an area of higher concentration to an area of lower concentration.

The bigger the concentration gradient, the faster the diffusion rate.

Concentration gradient: The difference in concentration.

Diffusion rate: How quick diffusion happens.

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Biology-B1: Osmosis

Osmosis is like diffusion but with water particles instead.

However it contains a semi-permeable membrane.

Osmosis: The movement of water molecules across a semi-permeable from a region at higher water concentration to a region of low water concentration.

Semi-permeable membrane: A membrane with small holes in which only small molecules can pass through them but not large molecules.

Osmosis can happen both ways.

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Biology-B1: Exchange surfaces

Organisms exchange substances with their enviroment. Cells can use diffusion to take in substances they need and get rid of  substances they don't need (waste products).


  • Oxygen and carbon dioxide are transferred between cells and enviroment during gas exchange

How easy it is for an organism to exchange substances depends on the organism's surface area to volume ratio (SA:V)

Prokaryotes have  large SA:V ratio so they can diffuse easily.

Multicellular organisms have smaller surface area compares to their volume. Their exchange surfaces are adapted to maximise effectiveness.

How are they adapted:

  • Thin membrane so substrances have short distance to diffuse.
  • Large surface area so lots of substances can diffuse at once.
  • Animals have a lot of blood vessels to get stuff into and out of blood quickly.
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Biology-B1: Exchange substances 1

Gas exchange happens in the lungs as it transfers oxygen to the blood and remove waste carbon dioxide. Gas exchange happens in the alveoli.

How are the alveoli specialised to maximise diffusion?

  • Enormous surface area
  • Very thin walls
  • Good blood supply

The inside of the small intestines are covered in villi:

The villi increase the surface area so digested food is absorbed more quickly into the blood.

How are the villis adapted:

  • Single layer of surface cells
  • Very good blood supply for quick absorption
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Biology-B1: Exchange substances 2

The structure of leaves allow gases to diffuse in and out. CO2 diffuses into the air space and diffuses into the cells where photosynthesis happens.

The underneath layer is an exchange surface covered in stomata.

Stomata: Where CO2 diffuse in through.

How is oxygen and water vapour diffused out?

Oxygen and water vapour diffuse out of the stomata.

What controls the stomata?

The stomata is controlled by the guard cells.

The flatten shape increases the area of the exchange surface. The walla of the cell form another exchange surface.

How do the air spaces help with the diffusion?

The air spaces inside the leaf increases the area of the surface so there is more chance for CO2 to get into the cells. 

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