2 Cells Flashcards
Structure of a typical plant cell
Cell membrane, cytoplasm, nucleus, mitochondria, cell wall, large vacuole and chloroplasts.
Structure of a typical animal cell
(also what plant and animal cells have in common)
Cell membrane, cytoplasm, nucleus, mitochondria.
Function of Cell membrane
Holds cell together and controls substances entering and leaving the cell.
Function of Cytoplasm
Supports many small cell structures and is where many different chemical processes happen, contains enzymes that speed up these reactions. Contains water and many solutes are dissolved in it.
Function of Nucleus
Contains genetic material in the chromosomes. These control how a cell grows and works. Nucleus also controls cell division.
Function of (plant) Cell wall.
Made of cellulose, gives extra support and defines its shape. Provides a semi-permeable surface for molecules to pass in and out of the cell.
Function of (plant) Vacuole
Contains cell sap. Used for storage of some materials, support shape of cell. If not enough cell sap in vacuole, plant may wilt.
Function of Chloroplasts
Contain the green pigment chlorophyll which absorbs the light energy that plants need to make food in the process known as photosynthesis.
Examples of specialised cells
Ciliated cells, red blood cells, sperm cells, egg cells in humans.
Root hair cells and palisade mesophyll cells in plants.
Structure and function of Ciliated cells
Cilia: tiny hair-like projections that cover the surface of certain types of cells. Can move and cell can coordinate movement to make waves that pass over the cell. Waves used to move mucus in trachea and bronchi. Tiny particles of dust or bacteria trapped in the mucus are carried along the flow. and pass up the tubes. They are then emptied into the oesophagus and swallowed into the stomach. This keeps lungs clean.
Structure and function of palisade mesophyll cells
Plant cells found in upper part of leaf. Most photosynthesis happens here.
Structure and function of red blood cells
They do not have a nucleus so cannot divide. Filled with haemoglobin which can pick up oxygen in the lungs and release it near the cells that need it deep inside the body. Biconcave shape so innermost part of red blood cell is never far away from outside, so diffusion in and out happens rapidly. Made in bone marrow and lasts 120 days before being destroyed in the spleen and liver.
Function and structure of human sperm cell
Relatively small compared to egg cell. Small vesicle of enzymes called acrosome at the tip of the cell. Enzymes of acrosome digest a hole in the egg cell membrane to allow nucleus of sperm cell to enter egg cell and fuse with its nucleus. Midpiece of sperm cell contains many mitochondria to provide energy to move the flagellum which powers the cell to move.
Function and structure of a human egg cell
Very large cell and almost visible without microscope. Cannot move on its own. Large amount of cytoplasm around nucleus provides nutrients for when the cell is fertilised and starts to divide.
Function and structure of root hair cells
Water and (dissolved) minerals absorbed by root hairs, very fine extensions of root hair cells on root surface, just behind growing tip of a root. Elongated shape increases surface area available for absorption. As they age, they develop waterproof layers and become non-functional.
Define diffusion
the net movement of particles from a region of their higher concentration to
a region of their lower concentration down a concentration gradient, as a result of their random movement.
Diffusion in cells and Examples
Particles that are small enough can move through cell membranes. These membranes are said to be partially permeable. Diffusion may happen more in one direction than the other depending on concentration.
Blood vessels in the lungs: oxygen from alveoli into red blood cells.
Carbon dioxide entering leaf cells.
Digested food substances from small intestine entering blood.
Define osmosis
the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane.
Explain what is meant by turgid or flaccid cells (in plants)
A turgid plant cell means that it is full of water. The pressure of water in cytoplasm against cell wall is called turgor pressure. Prevents more water entering plant by osmosis even if it is in a solution with a higher water concentration than in the cytoplasm. Prevents wilting of leaves.
A plant cell that is dehydrated is said to be plasmolysed. This is when the cytoplasm shrinks and the cell membrane pulls away from the cell wall leaving a gap between the wall and membrane. Leaves may wilt.
Explain plant uptake of water
Plant roots absorb soil water through osmosis since water concentration is lower in cytoplasm. The water molecules travel further into the root tissue until water molecules reach xylem vessels. The water molecules transported towards leaves. Transpiration from leaves helps draw water up to maintain concentration gradient between root cells and xylem vessels.
Explain effect of osmosis on animal cells
Animal cells also gain and lose water from osmosis. Effects can be more dramatic since they do not have a supporting cell wall. If you place an animal cell (e.g. red blood cell) into a solution of lower water potential, it will lose water by osmosis and become crenated.
