Cells and their organelles Achievement Standard 91160 Biology 2.8 Investigate biological material at the microscopic level

Living cells Living cells are divided into two types - prokaryotic and eukaryotic. This division is based on internal complexity. Basically, a prokaryotic cell is usually a single celled organism with no nuclear membrane. Cell Models

Similarities and differences

Plant Organelles Cell wall – semi-rigid structure outside the plasma membrane in plant cells. Mainly cellulose. Supports the cell and limits its volume. Cell (plasma) membrane – Inside the cell wall, controls entry and exist of materials. Cytoplasm – watery solution containing dissolved substances and enzymes. Chloroplasts – contain the green pigment chlorophyll. Used for photosynthesis. Mostly found in leaves. Nuclear membrane – a double layered membrane around the nucleus where chromosomes are found. Vacuole – Very large in plants – filled with aqueous solution of ions. Storage, waste disposal, growth.

Flagellum – A structure like a tail that helps movement of a cell – found in some reproductive plant cells. Mitochondria – Ovoid structures bound by a double membrane. Cell energy converters. Endoplasmic reticulum – network of tubules and flattened sacs, used for protein packaging. Chromosome – Found in the nucleus. Can genes. Cilia – small fibres on the outside of the cell used for movement.

Animal cell organelles The main organelles are mostly the same with the same functions. Some differences: No cell wall – the cells do not need to be supported as animals have skeletons No large water storage vacuole – they do have small ones. No chloroplasts – animals are consumers and do not need to photosynthesis.

Different animal cells and their organelles Nerve Cell – transmits nerve impulse to and from the brain. It has a long thin axon to allow the nerve impulse to travel and more mitochondria to give energy for the impulse

Muscle cell – helps muscles contract Muscle cell – helps muscles contract. A muscle cell is long and narrow so that the cells can group together to form a long narrow bundle of muscle tissue. They have more mitochondria to give it more energy to contract and provide movement.

Sperm cell – the reproductive cell of the male Sperm cell – the reproductive cell of the male. It swims to reach the female egg and fertilise it. It has a long tail (flagella) to do this. The large number of mitochondria in the tail release energy for the swimming motion.

White Blood cell – specialised for engulfing harmful bacteria White Blood cell – specialised for engulfing harmful bacteria. The blood cell has an irregular shape to allow it to flow around the bacteria. The lysosomes hold enzymes used to digest the bacteria.

Egg cell – The egg cell is round and has more cytoplasm than normal Egg cell – The egg cell is round and has more cytoplasm than normal. The cytoplasm acts as a food source for the developing zygote.

Lung cell – the cilia on the long thin lung cell move back and forth to move dust that has been breathed in up through the lungs to the throat where it can be swallowed.

Cross section of a leaf

Different plant cells and their specialisations Root Hair cell- The root hair cell in a plant has a long extension out the side into the soil. This means the cell membrane has a large surface area which can absorb more water by osmosis. Also within the root hair cell is a larger vacuole which allows for the increased water absorbed to be stored.

Pallisade cell – is the main photosynthetic cell of the leaf Pallisade cell – is the main photosynthetic cell of the leaf. They are long and thin and are close to the top of the leaf. Pallisade cells have many chloroplasts closely packed together. This provides a lot of chlorophyll which allows photosynthesis to occur.

Xylem cell – the xylem cell carries water from the roots, up the stem of a plant to the leaves where it is used for photosynthesis. The xylem cells are long, hollow tubes with no organelles. This allows water to move through them.

Guard cells – guard cells are found on the surface of leaves, usually the underneath. They control the movement of gases and water in and out of the leaf. They can change their shape to close the stoma (pore) to save water. They have chloroplasts in them to make their own food.