Cells, tissues and organ systems

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Lesson notes

Cell Structure and Function

All living things are made of **cells**, the basic unit of life.
Cells have specialised **organelles** that perform specific functions (e.g., nucleus, mitochondria).
The **cell membrane** controls what enters and leaves the cell.
**Plant cells** have a cell wall, chloroplasts and a large vacuole; animal cells do not.

Tissues

A **tissue** is a group of similar cells working together to perform a common function.
Examples: muscle tissue, nervous tissue, epithelial tissue, connective tissue.
In plants, tissues include **meristematic** (dividing) and **permanent** (mature) tissues.

Organs

An **organ** is made of different tissues working together for a specific job.
Examples: heart (pumps blood), lungs (gas exchange), stomach (digestion).
Plant organs include leaves (photosynthesis), stems (support/transport), roots (absorption).

Organ Systems

An **organ system** is a group of organs that work together to carry out a major body function.
Humans have 11 organ systems (e.g., respiratory, circulatory, digestive, nervous).
Some organs belong to more than one system (e.g., nose in respiratory and nervous).

Human Organ Systems Overview

**Respiratory system**: lungs, trachea; gas exchange (O₂ in, CO₂ out).
**Circulatory system**: heart, blood vessels; transports nutrients, gases, wastes.
**Digestive system**: stomach, intestines; breaks down food, absorbs nutrients.
**Nervous system**: brain, spinal cord, nerves; controls responses and coordination.
**Excretory system**: kidneys, bladder; removes waste from blood.
**Skeletal system**: bones; support, protection, movement.
**Muscular system**: muscles; movement, posture.
**Integumentary system**: skin; protection, temperature regulation.
**Endocrine system**: glands (e.g., thyroid, pancreas); hormone regulation.
**Lymphatic system**: lymph nodes, vessels; immunity, fluid balance.
**Reproductive system**: ovaries/testes; produces gametes, enables reproduction.

Plant Organ Systems

Vascular plants have two organ systems: **shoot system** and **root system**.
The **shoot system** (above ground) includes stems, leaves, flowers, and fruits.
The shoot absorbs light for photosynthesis and supports reproduction.
The **root system** (usually underground) anchors the plant and absorbs water and minerals.

Specialised Cells

**Specialised cells** have adaptations to perform specific functions.
Examples: red blood cells (biconcave, no nucleus for O₂ transport), nerve cells (long axons for signals), root hair cells (large surface area for water uptake).
Specialisation allows efficient division of labour in multicellular organisms.

Animal cell structure showing key organelles.

Plant cell with additional structures: cell wall, chloroplasts, large vacuole.

Examples of human organs and their organ systems.

Vascular plant showing shoot and root systems.

Slides

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Practice questions

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1.Which of the following is the correct order of biological organisation, from smallest to largest?
Easy
- Aorgan → tissue → cell → organ system
- Bcell → tissue → organ → organ system
- Ctissue → cell → organ → organ system
- Dcell → organ → tissue → organ system
2.What is the main function of the shoot system in vascular plants?
Easy
- Aabsorb water and minerals from the soil
- Banchor the plant in the ground
- Ccarry out photosynthesis and reproduction
- Dstore food and nutrients
3.Which of the following is NOT an organ system in humans?
Medium
- Aimmune system
- Bcirculatory system
- Cnervous system
- Dreproductive system
4.The nose is part of which two organ systems?
Medium
- Arespiratory and digestive
- Brespiratory and nervous
- Cnervous and circulatory
- Drespiratory and integumentary
5.How many distinct organ systems are there in the human body?
Hard
- A9
- B10
- C11
- D12
6.Which organ system includes the heart and blood vessels?
Easy
- Arespiratory system
- Bcirculatory system
- Cnervous system
- Dendocrine system
7.What is the primary function of the root system in plants?
Medium
- Aphotosynthesis
- Bsupport and reproduction
- Cabsorption of water and minerals
- Dtransport of sugars
8.Which of the following is true about organ systems in animals?
Hard
- AAll animals have exactly 11 organ systems.
- BSimpler animals may have fewer organ systems.
- COrgan systems are identical across all species.
- DPlants have more organ systems than animals.

Revision notes

## Cells, Tissues and Organ Systems ### Key Idea Structure and function are related at every level: cells → tissues → organs → organ systems. Specialised cells perform specific jobs; together they form tissues, which make up organs, which work in organ systems to keep an organism alive. ### Levels of Organisation 1. **Cells** – basic unit of life. Specialised cells (e.g., nerve cells, muscle cells, root hair cells) have unique shapes and parts to carry out particular functions. 2. **Tissues** – groups of similar cells working together (e.g., muscle tissue, nervous tissue, xylem tissue in plants). 3. **Organs** – structures made of different tissues that perform a specific function (e.g., heart, lungs, leaf, stem). 4. **Organ systems** – groups of organs that work together to perform one or more vital functions. ### Human Organ Systems (11 systems) - **Respiratory** – gas exchange (lungs, trachea) - **Digestive & Excretory** – breakdown of food and removal of wastes (stomach, intestines, kidneys) - **Circulatory** – transport of blood, nutrients, gases (heart, blood vessels) - **Urinary** – removal of liquid waste (kidneys, bladder) - **Integumentary** – protection (skin, hair, nails) - **Skeletal** – support and protection (bones) - **Muscular** – movement (muscles) - **Endocrine** – hormone production (glands) - **Lymphatic** – immunity and fluid balance (lymph nodes, spleen) - **Nervous** – control and communication (brain, spinal cord, nerves) - **Reproductive** – production of offspring (ovaries, testes) Note: Some organs belong to more than one system (e.g., nose is in respiratory and nervous systems). ### Plant Organ Systems (2 systems) 1. **Shoot system** – above ground: stems, leaves, flowers, fruits. Absorbs light for photosynthesis. 2. **Root system** – usually underground: roots. Anchors plant, absorbs water and minerals. ### Specialised Cells Examples - **Red blood cells** – biconcave shape, no nucleus → carry oxygen - **Root hair cells** – long extension → increase surface area for water absorption - **Palisade cells** – packed with chloroplasts → maximise photosynthesis ### Remember - Structure fits function: a cell’s shape and parts help it do its job. - Organ systems work together to keep the organism alive (e.g., circulatory system delivers oxygen from respiratory system to all cells).

Cell: The basic structural and functional unit of all living organisms.
Tissue: A group of similar cells that work together to perform a specific function.
Organ: A structure made of different tissues that performs a specific function.
Organ system: A group of organs that work together to perform one or more bodily functions.
Specialised cell: A cell adapted to carry out a particular function (e.g., nerve cell, muscle cell).
Shoot system: The above-ground organ system of vascular plants, consisting of stems, leaves, and reproductive parts.
Root system: The usually underground organ system of vascular plants that anchors the plant and absorbs water and minerals.

Flashcards

What is an organ system?

A biological system consisting of a group of organs that work together to perform one or more bodily functions.

How many organ systems are there in humans?

There are 11 distinct organ systems in humans.

List the 11 human organ systems.

Respiratory, digestive and excretory, circulatory, urinary, integumentary, skeletal, muscular, endocrine, lymphatic, nervous, and reproductive systems.

Is the immune system an organ system? Why?

No, because it is not composed of organs; it protects the body from infection but is not an organ system.

Give an example of an organ that belongs to more than one organ system.

The nose is in the respiratory system and also serves as a sensory organ in the nervous system.

What are the two major organ systems in vascular plants?

The shoot system and the root system.

What does the shoot system of a plant consist of?

Stems, leaves, and the reproductive parts (flowers and fruits).

What is the function of the shoot system?

It generally grows above ground and absorbs light needed for photosynthesis.

What does the root system do?

It supports the plant and absorbs water and minerals, usually underground.

Define a tissue.

A group of similar cells that work together to perform a specific function.

What is the relationship between cells, tissues, organs, and organ systems?

Cells form tissues, tissues form organs, and organs work together in organ systems.

What is a specialised cell?

A cell that has adapted a specific structure to perform a particular function in the body.

Name the organ system responsible for gas exchange.

The respiratory system.

Which organ system breaks down food and absorbs nutrients?

The digestive system (part of digestive and excretory system).

Which organ system transports blood and nutrients around the body?

The circulatory system.

Which organ system removes waste from the blood and produces urine?

The urinary system.

Which organ system protects the body and regulates temperature?

The integumentary system (skin, hair, nails).

Which organ system provides support and protection for organs?

The skeletal system.

Which organ system enables movement?

The muscular system.

Which organ system produces hormones?

The endocrine system.

Which organ system defends against infection and returns fluid to blood?

The lymphatic system.

Which organ system controls body activities via nerve impulses?

The nervous system.

Which organ system produces offspring?

The reproductive system.

Give an example of a specialised cell and its function.

Red blood cells are specialised to carry oxygen; nerve cells transmit electrical signals.

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