Biology note for unit 2- Edexcel

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  • Created on: 14-04-13 18:17
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Cells and organelles
Cells can be Eukaryotic or Prokaryotic
1)Eukaryotic cells are complex and include all animal and plant cells
2) Prokaryotes are smaller and simpler
Structure and function of organelles
Organelle Description Function
Nucleus A large organelle surrounded Chromatin is made from
by a nuclear envelope (double proteins and DNA. The pores
membrane) which contains allow substances e.g. RNA to
many pores. The nucleus move between the nucleus and
contains chromatin and often a the cytoplasm. The nucleolus
structure called the nucleolus. makes ribosomes.
Lysome A round organelle surrounded Contains digestive enzymes .
by a membrane with no clear These are kept separate from
internal structure. the cytoplasm by the
surrounding membrane, but
can be used to digest invading
cells or to break down worn
out components of the cell.
Vesicle A small fluid filled sac in the Transports substances in and
cytoplasm, surrounded by a out of the cell (via the cell
membrane. membrane) and between
organelles. Some are formed
by the Golgi apparatus or the
endoplasmic reticulum, while
others are formed at the cell
Ribosome A very small organelle that The site where proteins are
floats free in the cytoplasm or made.
is attached to the rough
endoplasmic reticulum.
Endoplasmic Reticulum (ER) There are two types: Smooth ER synthesises and
smooth is a system of processes lipids. The rough ER
membranes inclosing a fluid folds and processes proteins
filled space. the rough ER is that have been made at the
similar but covered in ribosomes.
Golgi apparatus A group of fluid filled flattened It processes and packages new
sacs. Vesicles are often seen at lipids and proteins. It also
the edge of the sac. makes lysomes.
Centriole Hollow cylinders containing a Involved with the separation of
ring of microtubules (tiny chromosomes during cell
protein cylinders) division.
Mitochondrion Usually oval shaped. They have Site of aerobic respiration
a double membrane ­ the inner where ATP is produced. Found
one is folded to form in large numbers in cells that
structures called cristae. Inside

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Prokaryotic cells are simpler than eukaryotic cells (they include bacteria and blue green algae).
Larger cells 2-200µm diameter Extremely small (less than 2.0µm diameter)
DNA is linear DNA is circular
Nucleus present ­ DNA inside nucleus No nucleus ­ DNA free in cytoplasm
No cell wall (in animals), cellulose cell wall (in Cell wall made of polysaccharide, but not
plants) or chitin cell wall (in fungi) cellulose or chitin.…read more

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Fibrous connective tissue ­ helps to force air back out of the lungs when exhaling
3) Blood vessels ­ capillaries surround the alveoli.
Organs are in systems
Organs work together to form organ systems ­ each system has a particular function.
For example, the respiratory system is made up of all the organs, tissues and cells involved in
breathing. The lungs, trachea, larynx, nose, mouth, and diaphragm are all part of the respiratory
system.…read more

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Root tips can be stained to observe mitosis
1. Cut the tip from a growing root (e.g. from a broad bean or garlic). Your root tip should be
about 5mm long.
2. Place the root tip in watch glass (a small shallow bowl) and add a few drops of hydrochloric
3. add a few drops of stain so that the chromosomes become darker and so easier to see
under a microscope. A stain that can be used is toluidine blue or acetic orecin.
4.…read more

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Egg cells are much larger than sperm cells
Cell division by meiosis
Meiosis is a type of cell division that happens in the reproductive organs to produce
Cells that divide by meiosis have the full number of chromosomes to start with, but the cells
formed have half the number.
Without meiosis , you would get double the genetic material when the gametes fused.
Stages of meiosis:
1. DNA replicates so there are two identical copies of each chromosome, called chromatids.
2.…read more

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The sperm head fuses with the cell membrane of the egg cell. This triggers a cortical
reaction ­ the egg releases the contents of vesicles called cortical granules into the
space between the cell membrane and the zone pellucida.
5. These chemicals from the cortical granules make the zona pellucida thicken, which
makes it impenetrable to other sperm which ensure the egg is only fertilised by one
6. One the sperm enters, the tail is discarded.
7.…read more

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Pluripotency ­ ability of a stem cell to produce all the specialised cells in an organism but
not extraembryonic cells.
Totipotent stem cells in humans are only present in the early life of an embryo ­ they
differentiate into extraembryonic cells and pluripotent stem cells. The pluripotent stem cells
then differentiate into specialised cells in the foetus.
Totipotency can be demonstrated in tissue culture
1) Plants also have stem cells ­ they are found in areas where the plant is growing e.g.…read more

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Stem cells in medicine
Stem cells can be used to treat some diseases
Stem cells can develop into any specialised cell, so scientists think they could be used to
replace damaged tissue in a range of diseases
Some stem cell therapies already exist.…read more

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Some people think only adult stem cells should be used as this doesn't involve the
destruction of life but they cannot develop into any cell.
The decision makers must take all the views into account when making important decisions
about scientific work that could save lives.
To help society make these decisions, regulatory authorities have been established to
consider the benefits and ethical issues.…read more

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Height is polygenic and affected by environmental factors, especially nutrition. E.g. tall parents
usually have tall children, but if the children are undernourished they won't grow to the maximum
Monoamine Oxidise A (MAOA) is an enzyme that breaks down monoamines (a type of chemical) in
humans. Low levels of MAOA have been linked to mental health problems.…read more




Aniso Osman

such good info thank youuu 

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