B3: Tissues and Organs

The cells that make up tissues are adapted for particular roles.

Muscular tissue is specialised to produce movement.

Glandular tissue is made up of cells which secrete (release) useful substances such as enzymes or hormones.

Multicellular organisms have many different cells which are specialised for a particular function, an advantage over single-celled organisms.

Some processes are easier for single-celled organisms, for example oxygen can easily diffuse into a single cell.

Multicellular organisms need a transport system to bring oxygen to every cell in their body. They also have specialised tissues that are adapted for allowing things to move in and out of the body quickly.

A system is a group of organs that performs a particular function.

The function of the digestive system is to break down the food you eat so the food molecules can enter the blood.

Remember! A group of cells is called a tissue. Organs are made up of different types of tissue. The heart contains muscle tissue that can contract and relax, nervous tissue to control the heart beat, and ligaments to hold the different tissues in place.

The whole of the digestive system is lined with epithelial tissue to protect the cells in the organs from digestive juices which could break them down.

The tissue secretes large quantities of mucus, which forms a barrier over the inner surface of the digestive organs. The mucus also makes it easier for the food to slide through the digestive system.

The organs in a plant are made up of tissues.

Plant organs include roots, stem, flowers and leaves. Each is made up of tissues such as mesophyll, xylem and phloem.

The whole plant is covered in a layer of epidermis. This helps to protect the underlying cells. stops the leaves from losing too much water and prevents pathogens from entering the plant.

Most of the cells in a leaf are mesophyll cells. This is where photosynthesis takes place.

Xylem and Phloem tubes run through the entire plant. These are tubes which make up the plant's transport system: xylem carries water from the roots to the leaves; sugars are transported around the plant in phloem.

The epidermal tissue on the lower surface of the leaf has little holes called stomata. These allow gases to diffuse into and out of the leaf.