Levels of organisation (multicellular organisms)

Section 1 from the Edexcel IGCSE Biology Specification - the nature and variety of living organisms

What are the levels of organisation?

organelles → cells → tissues → organs → organ systems → organism

What is the term given to organisms with cells that have their DNA enclosed in a nucleus?

Eukaryotic

Leaves are made of tissues. Define the term tissue.

These are groups of cells with similar structures that work together to perform a shared function.

What organelle is used to make proteins (protein synthesis)?

Ribosomes

Which organelle of a plant cell is filled with cell sap to help keep the cell turgid?

The large permanent vacuole

What are cell walls made of?

Cellulose

What is cell differentiation?

The process where a cell changes from one cell type to another to become specialised.

What are the cells which keep their ability to differentiate called?

Stem cells

What are the 2 types of stem cells and what is the main difference between them?

Embryonic stem cells: able to differentiate into any cell

Adult/tissue stem cells: able to differentiate into most, but not all, cells

Adult stem cells or embryonic stem cells can be used in medical treatments. Explain why the choice between the two types of stem cells can cause issues for doctors.

Embryonic stem cells can become any specialised cell type (so whatever is required can be obtained) but it may be rejected by the body. Adult stem cells limit what they can repair but they are generally safer and accepted by the immune system.

What are two ways stem cells can be harvested through?

Cloning or spare human embryos produced during IVF.

Suggest three advantages of using ES cells.

• are able to make any cell

• wasted embryos are now improving human lives

• will not be rejected by immune system if cloned (as they will be genetically identical)

Suggest five disadvantages of using ES cells?

• ethical concerns about killing a potential human

• reduction of efficient cloning as human embryos are delicate and hard to grow

• a lack of women donating their eggs, so less embryos and human eggs are obtained

• leftover embryos from IVF treatment can lead to rejection (by the immune system) as they are not genetically identical to the patient

there are others

Suggest 4 advantages of using adult stem cells.

• No embryos are killed so they have fewer ethical issues than ES cells

• Shortage of embryos or need for donors is not a concern

• They are partly differentiated and easier to control. They also have less chance of producing tumours.

• Using patients' own cells prevents rejection as the cells will be genetically identical.

Suggest 3 disadvantages of using adult stem cells.

• Stem cells taken from older people may not last very long as cells age.

• Adult stem cells are difficult to extract.

• Adult stem cells are limited in terms of cells they differentiate into. Nerve cells are very difficult to produce from adult stem cells, making it difficult to create therapies for spinal cord and brain repair.

One use of stem cells are heart cells to replace heart tissue damages due to what disease?

Coronary heart disease

Stem cells can be used to cure blindness. What cells are needed?

Retinal cells

What are induced pluripotent stem (iPS) cells?

adult cells that are reprogrammed to differentiate to become almost any specialised cell

Suggest one reason why iPS are so useful and important.

Since they come from adult cells, they carry the genetics of the donor. This allows labs to capture the genomes of real disorders so they can work with the cells to find real cures.

Fill in the blank

"________ means cells that can differentiate to become almost any type of specialised cell or tissue in the body."

Pluripotent