2.6 Cell division, cell diversity and cellular organisation Flashcards
What are the 4 phases of the cell cycle?
G1, S, G2, M
What does each phase do?
G1 and G2, are growth phases and the S phase is when DNA is synthesised. This is called interphase, cells spend most of the cell cycle in this. The M phase is mitosis.
Do all cells go through mitosis?
No, not all cells go through mitosis. Some stop at the checkpoints because there is something wrong in the cell. Other times, the cell rests in the G1 phase.
How may times do cells go through the cell cycle?
Most go through it a finite amount of times. The exact depends on the cell type and is called the Hayflick limit. Only stem cells and tumour cells have no Hayflick limit. These cells are known as immortal because they go on dividing indefinitely.
How is the cycle regulated?
The cell cycle has several checkpoints where the DNA of the cell is checked. If the DNA is undamaged, the cell will be allowed to go through to the next phase. The two main checkpoints are the G1/S checkpoint and the G2/M checkpoint. Here, a regulatory protein called p53 checks the DNA for damage, such as mismatched bases or mutations. p53 is a tumour suppressor gene. It prevents mutated cells from dividing and becoming cancerous. if p53 itself is mutated, then cells will pass through these checkpoints without being checked and can quickly become cancerous.
What is the g) phase?
Sometimes cells enter a phase from the G1, phase called G0. During this phase, cells can undergo differentiation or senescence (cells no longer divide). Cells can also undergo programmed cell death (apoptosis).
What are guard cells?
They are found on the underside of the lead. They come in pairs, and control the opening and closing of the stomata.
What are palisade cells?
They are found near the top surface of the leaf. They are long and thin so that many cells can be packed close together. They are filled with chloroplasts to absorb sunlight for photosynthesis.
What are root hair cells?
They are found in the roots. They have long thin hairs to increase their surface area for taking up water and minerals from the soil.
What makes the xylem specialised?
Xylem tissue transports water and minerals from the roots to the top of the plant. It is made of many sieve elements joined end to end, separated by sieve plates. Phloem is living tissue, but supported by companion cells.
What makes the phloem specialised?
Phloem tissue transports sugars (mainly sucrose0 and other assimilates up and down the plant. Its made of many sieve elements joined end to end, separated by sieve plates. Phloem is living tissue, but supported by companion cells.
What are organ systems?
A number of organs working together to carry out an overall life function.
What organs are part of the digestive system?
Oesophagus, stomach, intestines plus associated glands, liver and pancreas.
What life processes does the digestive system carry out?
Nutrition to provide ATP and materials for growth and repair.
What organs are part of the circulatory system?
Heart and blood vessels.
