Title: Summary Notes - Topic 2 Organisation of the Organism - CIE Biology IGCSE
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CIE Biology GCSE
# 2: Organisation of the organism
# Notes www.pmt.education Cells can be viewed using a microscope to study their structure. Plant and animal cells are known as eukaryotic cells as they contain a nucleus and membrane bound organelles such as ribosomes and mitochondria. Bacteria are known as prokaryotes as they do not contain these. They also do not contain a rough endoplasmic reticulum .
To calculate the size of a specimen under a microscope:
Where the image size is the size the specimen appears when viewed through the microscope.
Functions of eukaryotic cell structures:
Cytoplasm - A jelly-like material within the cell in which reactions occur. The cytoplasm contains structures such as ribosomes and vesicles.
Cell membrane - a thin membrane that surrounds the cell, controls entry and exit of substances.
Nucleus and DNA - the nucleus contains genetic material in the form of DNA which codes for proteins. DNA replication also occurs in the nucleus.
Ribosomes and rough endoplasmic reticulum (RER) - The RER surrounds the nucleus and ribosomes are attached to it. Ribosomes are the site of protein synthesis.
Mitochondria - site of respiration. Provides energy for the cell to function.
Vesicles - used to transport materials in the cell.
In addition to these, plant cells also contain a vacuole, chloroplasts and are surrounded by a
cell wall .
Vacuole - is a fluid-filled sac containing mineral salts, sugars, amino acids, waste substances and pigments which colour the cell and attract pollinating insects .
Chloroplasts - are the site of photosynthesis , which allows plants to convert light energy to glucose .
Cell wall - gives the cell structure and prevents bursting . It also controls what enters and exits the cell. www.pmt.education Levels of organisation
Key terms:
Tissue - a group of similar cells working together to carry out a particular process
Organ - a group of tissues working together to carry out a specific function
Organ system - a group of related organs working together to carry out functions in the body
Specialised cells:
Cells and tissues are specialised to carry out their particular function. Examples of specialised cells are:
Ciliated cells - ciliated cells are found lining the trachea . They have hair-like projections called cilia which move together to transport mucus, dust and bacteria upwards to the throat.
Root hair cells - are adapted to have a large surface area . This speeds up the rate of osmosis and mineral ion uptake in plants.
Xylem vessels - used to transport water through plants in transpiration . The xylem is made from hollowed-out dead cells that have the ends removed to make a tube for water to pass through. They have a thick cell wall to provide structural strength and are
thin to allow capillary action .
Palisade mesophyll cells - this is where photosynthesis occurs. Mesophyll cells are tall and closely packed to efficiently absorb light and contain lots of chloroplasts for photosynthesis. They are also placed at the top of the leaf where most of the light hits enabling them to absorb much light energy as possible.
Nerve cells - nerve cells are adapted to rapidly transmit electrical impulses. Nerve cells are myelinated , which insulates the cell and prevents the impulse weakening and slowing down. They also contain lots of mitochondria to provide energy. Dendrites have a large surface area and are branched to receive impulses from many other neurons.
Red blood cells - red blood cells contain haemoglobin which allows them to carry oxygen around the body. They have a biconcave shape which increases their surface area, allowing for rapid diffusion. They also have thin cell membranes to decrease the diffusion distance. They do not contain a nucleus , thus have more space for oxygen. www.pmt.education Sperm cells - sperm cells are adapted by containing lots of mitochondria so that the cell has enough energy to reach the egg cell. It has a tail to allow movement and contains
digestive enzymes to help penetrate the egg cell membrane. www.pmt.education