Specialised cells, tissues, organs and systemsIB MYP Sciences: Revision notes
Section 1
Levels of organisation
Living things are organised in levels, from smallest to largest:
cell → tissue → organ → organ system → organism
- A tissue is a group of similar cells that work together to do a job.
- An organ is made of several different tissues working together.
- An organ system is a group of organs working together to do a major job.
- An organism is a whole living thing.
Section 2
Specialised animal cells
A specialised cell has a structure that suits its function.
- Red blood cell: contains haemoglobin to carry oxygen, and has no nucleus, so there is more room for haemoglobin.
- Sperm cell: has a tail to swim and many mitochondria to release energy for swimming. Its head carries DNA.
- Egg cell: large, with a food store in the cytoplasm, and carries DNA.
- Nerve cell: long and thin, so it carries electrical impulses over long distances.
- Muscle cell: can contract (get shorter) to cause movement, and has many mitochondria for energy.
Name the feature, then say what it does. 'The tail helps the sperm swim' earns the mark, not just 'it has a tail'.
Section 3
Specialised plant cells
- Root hair cell: has a long, thin extension that gives a large surface area to absorb water and minerals from the soil. It has no chloroplasts.
- Palisade cell: tall and packed with chloroplasts to absorb light for photosynthesis. Palisade cells are found near the top of the leaf.
Both cells have a cell wall, which supports them.
Section 4
Tissues and organs
Examples of tissues: muscle tissue (contracts), glandular tissue (makes juices such as digestive enzymes) and, in plants, palisade tissue.
Examples of organs:
- The stomach is made of muscle tissue, glandular tissue and a protective lining. It churns food and makes digestive juices.
- The leaf is made of protective tissue, palisade tissue and transport tissue in the veins. It makes food by photosynthesis.
An organ is not just 'lots of cells'. It must contain several different tissues working together.
Section 5
Organ systems
An organ system is a group of organs that work together. The digestive system includes the mouth, stomach, small intestine and large intestine. It breaks down food so that it can be absorbed.
Other examples are the circulatory system (heart and blood vessels) and the nervous system (brain, spinal cord and nerves).
In plants, the leaves and stem form the shoot system, and the roots form the root system.
Must know
- Levels: cell, tissue, organ, organ system, organism
- Tissue: similar cells; organ: several tissues; organ system: several organs
- Red blood cell: haemoglobin, no nucleus. Sperm: tail, mitochondria. Nerve: long. Muscle: contracts.
- Root hair cell: large surface area. Palisade cell: many chloroplasts.
- Examples: stomach (organ), leaf (organ), digestive system (organ system)
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Specialised cells, tissues, organs and systems
- A doctor in Riyadh explains to a class how the human body is organised, using the stomach as an example. The stomach wall contains muscle tissue that churns food, glandular tissue that makes digestive juices, and a lining of protective cells. The stomach is part of the digestive system.Explain why the stomach is called an organ rather than a tissue.2 marks
- A student is comparing specialised cells in humans and plants, including red blood cells, sperm cells and the root hair cells of a seedling.Explain how the structure of a red blood cell makes it suited to carrying oxygen.2 marks
- Biologists in Brazil study the structure of a leaf. The leaf has a protective layer of cells on its surface, palisade cells just below the upper surface where most photosynthesis takes place, and veins that carry water and sugars through the leaf.Describe how a palisade cell is adapted for photosynthesis.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).