Tissues, organs and organ systemsIB MYP Biology: Revision notes
Section 1
Levels of organisation
Living things are organised in levels, from smallest to largest:
cell → tissue → organ → organ system → organism
- A cell is the basic unit of life.
- A tissue is a group of similar cells working together.
- An organ is a group of different tissues working together to do a job.
- An organ system is a group of organs working together.
- An organism is a living thing made of organ systems working together.
Do not mix up the levels. An organ is made of different tissues. An organ system is made of different organs.
Section 2
Example: the stomach
The stomach is an organ because it is made of several tissues working together to digest food:
- Muscular tissue churns the food.
- Glandular tissue makes digestive juices.
- Epithelial tissue covers the inside and outside surfaces.
To show a structure is an organ, say it is made of different tissues that work together to do one job.
Section 3
Human organ systems
- Digestive system: stomach, small intestine, liver, pancreas and more. It breaks down food into small soluble molecules and absorbs them into the blood.
- Circulatory system: heart, blood vessels and blood. It transports oxygen, nutrients and waste around the body.
- Respiratory system: lungs and airways. It takes in oxygen and removes carbon dioxide (gas exchange).
- Nervous system: brain, spinal cord and nerves. It carries electrical impulses and coordinates the body's responses.
Systems work together. For example, the respiratory system takes in oxygen and the circulatory system delivers it to the muscles.
Blood is a tissue (different cells in a liquid), the heart is an organ, and the circulatory system is an organ system.
Section 4
Plant organs and systems
Plants are organised in the same way.
- The leaf is an organ. It is made of tissues such as the epidermis, palisade tissue (photosynthesis), spongy tissue, and xylem and phloem (transport).
- The root is an organ. It anchors the plant and absorbs water and mineral ions.
- The stem is an organ. It supports the plant and its xylem and phloem transport substances.
- The shoot system (stem, leaves and flowers) and the root system are plant organ systems that work together.
Water travels up through xylem tissue from the roots to the leaves.
Must Know
- Order: cell, tissue, organ, organ system, organism
- Tissue: similar cells. Organ: different tissues
- Stomach: muscular, glandular and epithelial tissue
- Digestive, circulatory, respiratory and nervous systems
- Plants: leaf, root, shoot
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Tissues, organs and organ systems
- The human stomach is an organ. Its wall contains muscle tissue that churns the food, glandular tissue that makes digestive juices, and epithelial tissue that covers the inside and outside surfaces.Explain why the stomach is classed as an organ rather than a tissue.2 marks
- A student is making a revision poster about the human circulatory system. It includes the heart, the blood vessels and the blood, which together carry oxygen, nutrients and waste around the body.Describe the function of the circulatory system and of the respiratory system.2 marks
- A student wants to find out how fast water moves up a plant stem. She places identical celery stalks, each with leaves at the top, in beakers of water containing red food dye. She removes one stalk after 1 hour, one after 2 hours and one after 3 hours, and cuts across each stalk to look for the dye.State a testable hypothesis for the investigation, with a scientific reason, and identify the independent variable.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).