Chapter 1: Cells – the Basic Building Blocks of Life

Lesson 7: Understanding Organisation in Multicellular Organisms Define the terms tissues, organs and organ systems. Explain the organisational structure in multicellular organisms. Compare the strengths and weaknesses of multicellular organisms and ­single-­celled organisms. Did you know? There are 15 different organ systems within human beings, all working together to help us to survive.

Lesson 7: Understanding Multicellular Organisms

Lesson 7: Cells, tissues and organs Tissues: groups of similar specialised cells working together Examples of human tissues are muscles and bones. Organ: different tissues working together Every organ has a specific job – the eye is an organ made up of many different tissues including a lens and an iris. They work together to enable us to see. Examples of other organs are: the heart, which pumps blood to the cells the kidneys, which clean the body and balance water in the body the brain, which allows us to control all parts of our body quickly. Organ systems: made up of organs that work together. Examples of the organ systems are: the circulatory system, the skeletal system, the respiratory system, the digestive system, the reproductive system and the nervous system.

Lesson 7: Cells, Tissues, Organs Cells – Tissues – Organs – Organ System

Lesson 7: How cell types evolved Some cells evolved to join and work together, forming groups of cells. An advantage of this was that in times of food shortage, food could be caught, digested and shared more effectively by cells working together. Eventually some of the cells within the group became specialised and took on particular jobs. This eventually led to the formation of simple multicellular organisms. These could grow to be much larger than the unicellular organisms and so were better protected and could move further in search of food. However, they needed to evolve complex organ systems in order to become much larger. This requires a lot of energy, and the larger the organism became, the slower the rate of reproduction.

Lesson 7: Key Vocabulary and Notes Key Vocabulary: tissue, organ, organ system Key Notes: Organ systems are made from organs which are made from tissues which are made from cells! Multicellular organisms are made from organisms working together Multicellular organisms are larger than unicellular organisms The larger the organisms the slower the rate of reproduction

Lesson 7: Questions and Answers 1. Name three organs and describe their function Ans: the heart, which pumps blood to the cells the kidneys, which clean the body and balance water in the body the brain, which allows us to control all parts of our body quickly 2. Describe the organisation of the multicellular organisms. (using: tissue, organ system, cell, organ) Ans: cell, tissue, organ, organ system 3. What is one advantage of multicellular organisms over unicellular organisms? Ans: Multicellular organisms can grow larger to be able to protect themselves better.