Year 7 · From cells to whole organisms

Learn the idea

In a multicellular organism, specialised cells carry out particular jobs. A tissue is a group of cells working together for a function. An organ contains different tissues working together. An organ system contains organs that cooperate. The organism is the complete living individual. These levels describe organisation, not a simple increase in image size.

Tissues working inside organs

Muscle tissue can contract; nervous tissue carries signals. The heart contains muscle tissue along with other tissues that enable it to pump blood. A leaf is a plant organ containing different tissues, including photosynthetic and transport tissues. A chloroplast is a cell structure, so calling it an organ confuses levels.

Transport and gas exchange

The heart pumps blood through vessels in the circulatory system. The lungs exchange gases between air and blood. These organs cooperate: oxygen entering blood in the lungs is transported to tissues. An organ performs its own role within connected systems; the lungs do not pump blood and the heart does not make oxygen.

Processing food and removing wastes

The stomach mixes food and begins some digestion; much digestion and nutrient absorption occur in the small intestine. The large intestine absorbs remaining water and forms faeces. The liver processes absorbed nutrients and makes bile. Kidneys filter blood and adjust water and dissolved substances while forming urine. Egestion means passing undigested material as faeces. Excretion removes wastes from cell processes; these are different jobs.

Control, support and movement

The brain and nerves form part of the nervous system, receiving information and coordinating responses. A skeleton supports and protects structures; muscles pull on bones to create movement at joints. Skin forms a protective boundary and contributes to sensing and temperature control. A named function is a learning model, not a way to diagnose illness.

Systems cooperate

During ordinary movement, muscles use energy, the circulatory system transports substances, and breathing supports gas exchange. The nervous system coordinates actions. A diagram with one system highlighted has not shown every participating system. Explain links using supplied information rather than making personal health or fitness judgments.

Compare other vertebrates

Vertebrates share an internal skeleton with a backbone, but their organs are adapted to different lives. A typical fish has gills for gas exchange in water, while a bird uses lungs with a distinctive air-flow arrangement. Both have hearts that circulate blood. Do not replace a fish gill label with a human lung label just because both exchange gases.

Reason from a supplied model

An unfamiliar vertebrate diagram may show a pumping organ connected to vessels and a gas-exchange surface. Those links support a circulatory role, but a shape alone does not establish every function. Compare similarities, differences and missing evidence. For a plant comparison use roots, stems and leaves, rather than forcing human organ names onto it.

Common mistake

An organ is not just a very large cell. Different tissues cooperate within an organ, and organs cooperate within systems.

A plant example

Root cells form tissues within a root organ. Roots, stems and leaves cooperate in a whole plant; this is an organisation model that does not need human organ names.

Interpreting an incomplete diagram

A bird diagram with lungs and a heart supports separate gas-exchange and pumping roles. It is not detailed enough to describe its whole respiratory air-flow system.

Your written practice

Show your working on paper and enter your answer here. If it does not match, compare the model and try again.