Cells

What is a cell?

What is a cell? A cell is the smallest unit of living things. Cells are microscopic in size. The parts or organelles that make up a cell can only be observed using a microscope.

Animal and plant cells The two kinds you need to be most familiar with are ‘typical’ animal and plant cells.

Cell membrane One part found in all cells is the cell membrane.

Cell membrane The cell membrane controls what chemicals can enter and leave the cell.

Nucleus Another part found in all cells is the nucleus.

Nucleus The nucleus is the ‘control centre’ of the cell. It contains DNA and controls all the activities of the cell.

Cytoplasm All cells also contain cytoplasm.

Cytoplasm Cytoplasm is a jelly-like mixture of chemicals where most of the chemical reactions we need to keep us alive take place.

Mitochondrion (plural – mitochondria) All cells also contain mitochondria.

Mitochondria Mitochondria are the ‘power houses’ of the cell. These are the sites where respiration taes place and energy is released from our food.

Plant cell organelles Plant cells may contain some extra parts.

Chloroplasts (plant cells) Chloroplasts which are disc shaped and are the ‘sites for photosynthesis’. They contain the green pigment chlorophyll which is needed for photosynthesis.

Cell wall (plant cells) A cell wall which is a rigid outer layer to support the cell and give it shape.

Vacuole (plant cells) Large permanent vacuoles are found in plant cells. These store a liquid called cell sap (a mixture of sugars, salts and water). These help to support the plant structure.

A cell is like a city.

A plant cell compared to a city The wall of a city provides a fixed boundary. The cell wall acts like the wall of the a city. It gives the plant cell a fixed shape.

A plant cell compared to a city The border guard of a city controls who enters or leaves the city. The cell membrane controls what enters or leaves the cell.

A plant cell compared to a city The air, land and water provide a physical environment where all the the components of the city can exist. The cytoplasm of the cell is the place where all of the organelles are found.

A plant cell compared to a city The office where the city’s leader is based (e.g. city hall) controls what happens in the city. The nucleus controls the activities if the cell.

A plant cell compared to a city The power plant provides electrical energy for the city. The mitochondria of the cell provide the energy needed for the cells activities.

A plant cell compared to a city The restaurants within a city make food for the people in the city. The chloroplasts are the sites where food is made in plant cells.

A plant cell compared to a city The reservoir of a city stores water. The large permanent vacuole of a plant cell stores cell sap.

Animal and plant cells The two kinds you need to be most familiar with are ‘typical’ animal and plant cells.

Unicellular Organisms A single cellular organism performs all required functions in one cell. e.g. Amoeba.

Multicellular Organisms Multicellular organisms are made up of more than one type of cell. Their bodies need to supply food and nutrients, transport materials, remove wastes and fight infection.

What do all of these cells have in common?

Cell Specialisation The cells on the previous slide all have typical structures such as: cytoplasm cell membrane cell wall nucleus chloroplasts However, the structure each type of cell is different so that it can carry out a particular function. This is known as cell specialisation.

Head contains nucleus and mitochondria Sperm cell Head contains nucleus and mitochondria Tail Sperm cells swim towards the egg to carry out fertilisation. They have a tail to enable them to swim and many mitochondia for producing energy.

Egg cell (ovum) Made in the ovaries of mammals. Cytoplasm containing food store Made in the ovaries of mammals. An egg cell is large compared to sperm. Contains a food store in the cytoplasm for nourishing the embryo. Nucleus

Ciliated cell nucleus Help to prevent dust and bacteria entering lungs Line the windpipe (trachea) Have tiny hairs called cilia Cilia sweep mucus with trapped dust and bacteria up to mouth to be swallowed cilia

Nerve cell (neurone) Longest cells in the body extension of the cytoplasm (axon) nucleus Longest cells in the body Transmit electrical nerve impulses in body

Red blood cell No nucleus Contain haemoglobin to carry oxygen around the body “Biconcave” shape for large surface area

Palisade mesophyll cell Found in leaves of plants Packed with chloroplasts to trap light for photosynthesis nucleus chloroplasts

Root hair cell Root hair increases surface area for uptake of water and minerals from soil Thin cell wall so water can move in easily thin cell wall root hair cell membrane vacuole

Tissues Tissues are groups of cells that perform the same function. Examples of human tissues include epithelial tissue and muscle tissue.

Epithelial tissue Epithelial tissue covers body surfaces and lines cavities and tubes. These include the airways and digestive tract. Some epithelial tissue is specialised to form glands like oil and sweat glands in the skin.

Muscle tissue Muscle tissue helps in body movement because it can contract and relax. There are three different types of muscle tissue: cardiac skeletal smooth

Plant tissues Plants also have different types of cells that are grouped together into tissues. In each case, the structure of each cell is related to its function. Plant tissues include epidermal, palisade mesophyll and spongy mesophyll.

Epidermal tissue Epidermal cells fit together like a jigsaw From Greek word meaning “over-skin” Create a strong and protective layer on the outside of leaves, roots and stems epidermal

Palisade mesophyll tissue These cells have many chloroplasts to trap light for photosynthesis Are column shaped so that they can be densely packed near the surface of the leaf palisade mesophyll

Spongy mesophyll tissue These cells have a rounded shape This allows them to be loosely arranged so that they can take up carbon dioxide by diffusion Carbon dioxide can then be used for photosynthesis spongy mesophyll

Organs A group of tissues working together form an organ. Examples of animal organs include the heart, lungs, brain and kidneys. Examples of plant organs include roots, stems, flowers, seeds and fruits.

Systems A group of related tissues and organs eg. blood, heart, arteries, capillaries and veins make up a system. The tissues an organs above make up the circulatory system.

Systems Examples or organ systems in animals include: skeletal muscular digestive respiratory nervous circulatory

Systems Examples of organ systems in plants include the vascular system in the roots and shoots. This includes xylem and phloem. You will learn about these specialised cells later.

Summary Cells have different ___________ that allow them to carry out a particular__________. These are known as cell specialisations. Many __________ cells working together form a __________. A group of tissues that work together form an ___________. Organs are found in both _______ and plants. A group of related tissues and organs form a __________. animal specialised organ tissue structures function system

Summary Cells have different _________ that allow them to carry out a particular__________. These are known as cell specialisations. Many __________ cells working together form a ______. A group of tissues that work together form an _______. Organs are found in both _______ and plants. A group of related tissues and organs form a __________. structures function specialised tissue organ animal system

Building cells Refer to the attachment – ‘Cell Project’ to find out about your group assignment on cells. Oh no!