B2 Flashcards
What is the cell cycle?
Cells in the body divide to produce more cells, so that the body can grow and replace damaged cells. Cells grow and divide over and over again.
What are the four growth stages in the cell cycle?
Mitosis, Gap Phase 1 (cell grows and new cell structures and proteins are made), Synthesis (cells replicates its DNA, so that when it splits during mitosis the two new cells will contain identical DNA) and Gap Phase 2 (cells keep growing and proteins needed for cell division are made)
What happens during synthesis?
The molecule of DNA splits. Bases on the free-floating nucleotides pair up with matching bases on the DNA. Cross links form between the new nucleotide bases and the old DNA, and the new nucleotides join together. Two new DNA molecules identical to the original one are formed.
What is mitosis?
It is when a cell reproduces itself by splitting to form two identical offspring.
What happens during mitosis?
A cell has two copies of its DNA all spread out in long strings. Before it divides, the DNA forms X-shaped chromosomes. Each “arm” of a chromosome is identical to the other. They line up at the center of the cell and cell fibres pull them apart. Membranes form around each of the sets of chromosomes. These become the nuclei of the new cells and the cytoplasm divides.
What is differentiation?
The process by which a cell changes to become specialized for its job. Having specialized cells is important as it allows organisms to work more efficiently.
What are palisade leaf cells?
They do most of the photosynthesis in plants, so they are packed with chloroplasts. Their tall shape means they have a lot of surface area exposed which absorbs CO2 from the air. Their thin shape means that you can fit loads of them at the top of a leaf, and they’re near the light.
What is sperm?
The function of sperm is to get the male DNA to the female DNA during reproduction. Sperm have long tails and streamlined heads to help them swim, they contain lots of mitochondria to provide them with energy, and they have enzymes in their heads to digest through the egg cell membrane.
What are stem cells?
Stem cells are undifferentiated. Depending on what instructions they’re given, they can divide by mitosis to become new cells, which then differentiate.
What are embryonic stem cells?
They are found in early human embryos. They have the potential to turn into any kind of cell. All of the cells in the human body have to come from the few cells in the embryo.
Where are stem cells found in adults?
They are found in certain places, like bone marrow. These stem cells aren’t as versatile as embryonic stem cells - they can’t turn into any cell type, only certain ones from the tissue they originally came from.
What cells divide by mitosis in plants?
Only cells which are found in plant tissues known as meristems. Meristem tissue is found in the area of a plant where it is growing - eg. roots and shoots.
What do meristems produce?
Unspecialized cells that are able to divide and form any cell type in the plant - they act like embryonic stem cells. Unlike human stem cells, these cells can divide to generate any type of cell for as long as the plant lives.
What is diffusion?
The net movement of particles from an area of higher concentration to an area of lower concentration.
What do cell membranes do?
They allow substances in and out of a cell through diffusion, active transport and osmosis. Only very small molecules can diffuse through cell membranes.
What is active transport?
The movement of particles across a membrane from an area of lower to an area of higher concentration using energy released from respiration.
What is osmosis?
The net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration.
What is a partially permeable membrane?
A membrane with holes in it with very small holes in it (a cell membrane is a partially permeable membrane)
What is water potential?
The likelihood of water molecules to diffuse out of or into a solution. eg If a solution has a higher water potential, it has a high concentration of water molecules.
What does it mean when a plant cell becomes turgid?
Watering a plant increases the water potential of the soil around it, meaning that all of the plant cells draw water in by osmosis until they become turgid (plump and swollen). The contents of the cell push against the cell wall - this is called turgor pressure which supports plant tissues.
What does it mean when a plant cell becomes flaccid?
If there’s no water in the soil, a plant starts to wilt. This is because the cells become flaccid - they lose water. The plant wouldn’t totally lose its shape as the inelastic cell wall keeps things in position.
