Exploring Life Chapter Notes | Preparation for EmSAT Grade 4 PDF Download

Introduction

The chapter "Exploring Life" helps us understand what makes something a living thing and how living things are different from nonliving things. It explains that all living things are made of cells, which are like tiny building blocks. The chapter also talks about the seven characteristics that all living things share, such as growing, reproducing, and using energy. We learn about the history of microscopes, how they helped scientists discover cells, and how cells are different in various living things. This chapter also introduces the classification of living things into domains and kingdoms and explains why viruses are not considered living things.

What are living things?

• Living things are organisms that have specific traits, such as being made of cells.
• Nonliving things, like a flame, do not have all the characteristics of living things.
• We can tell if something is living by checking if it has all the traits of life.

Building Blocks of Life

• All living things are made of cells, which are the smallest units of life.
• Cells are tiny and can only be seen with a microscope.
• Cells perform different jobs to keep living things alive.
• Nonliving things, like salt, do not have cells.

Technology Leads to Discovery

• Microscopes are tools that make tiny things like cells look bigger.
• Early scientists couldn’t see cells until microscopes were invented.
• Microscopes are like telescopes, but they help us see small things instead of faraway planets.

Did You Know?

• Robert Hooke’s Discovery
  • Over 300 years ago, Robert Hooke used a microscope to discover cells.
  • He looked at a thin slice of cork and saw tiny spaces that looked like a honeycomb.
  • He called these spaces “cells” because they reminded him of small rooms.
  • His discovery showed that living things are made of cells.
• Anton van Leeuwenhoek
  • In the late 1600s, Anton van Leeuwenhoek made better microscopes.
  • His microscope could make things look 270 times bigger.
  • He used it to see tiny organisms in pond water and blood.
  • His work helped scientists learn more about cells.

Discovering the Cell Theory

• The cell theory was created by combining observations from different scientists.
• The cell theory has three main principles:
  • All living things are made of cells.
  • Cells are the smallest unit of life and perform different functions to keep organisms alive.
  • All cells come from other cells through cell division.
• Atoms combine to form molecules, and molecules make up cells.

Principles of the Cell Theory 

• All matter is made of atoms.
• Atoms join together to form molecules.
• Molecules build up cells.
• All living organisms are made of cells.
• Cells are the smallest units of life.
• Cells carry out various functions to keep organisms alive.
• New cells are formed only from existing cells through cell division.

Did You Know?

Microscopes Today

• Light microscopes use light and lenses to make objects look up to 1,500 times bigger.
• Some objects, like blood cells, need to be stained with dye to see details in a light microscope.
• Electron microscopes use electrons and can magnify objects up to 100,000 times or more.
• There are two types of electron microscopes:
  • Transmission Electron Microscopes (TEMs): Electrons pass through the object to show tiny cell structures.
  • Scanning Electron Microscopes (SEMs): Electrons bounce off the object to create a 3D image of its surface.

How many cells do living things have?

Living things can be unicellular (made of one cell) or multicellular (made of many cells):

• Unicellular organisms, like paramecium, have one cell that does all the jobs needed to live.
• Multicellular organisms, like mice or blue whales, have many cells that work together. In multicellular organisms, cells are organized into groups with special jobs, like muscle cells for movement or cells for digestion.

Common Characteristics

• All living things share seven characteristics that make them different from nonliving things.
• These are: being made of cells, organization, growth and development, reproduction, response to stimuli, maintaining internal conditions, and using energy.

Characteristics of Life

• All living things share seven characteristics:
  • Organization: Living things have structures that work together, from simple unicellular organisms to complex multicellular ones.
  • Growth and Development: Growth means getting bigger, and development means changing during life, like a caterpillar turning into a butterfly.
  • Reproduction: Living things make new living things. There are different types of reproduction, like producing seeds or giving birth.
  • Response to Stimuli: Living things react to changes (stimuli) in their environment, like moving toward light or feeling hungry (internal stimuli).
  • Maintaining Internal Conditions (Homeostasis): Living things keep their insides stable, like maintaining body temperature, even when the outside changes.
  • Using Energy: Living things need energy to live. Plants get energy from the sun, while animals get energy by eating food.
  • Made of Cells: All living things are made of cells, which are the basic units of life.
• If something does not have all these characteristics, it is not a living thing.

What are the different types of cells?

Cells are divided into two types: prokaryotic and eukaryotic.

1. Prokaryotic Cells:
   • Do not have a lining around their genetic material.
   • Are smaller and have fewer parts than eukaryotic cells.
   • Most are unicellular organisms called prokaryotes, like bacteria.
   • Some live in groups called colonies or in extreme environments.
2. Eukaryotic Cells:
   • Have a lining around their genetic material.
   • Have organelles (special parts) with specific jobs, most surrounded by linings.
   • Are larger than prokaryotic cells.
   • Found in plants, animals, fungi, and protists, which are called eukaryotes.

Classification of Organisms

• Organisms are classified by their cell type (prokaryotic or eukaryotic) and other features.
• All organisms are grouped into three domains: Bacteria, Archaea, and Eukarya.
• Domains are further divided into six kingdoms.
• Classification uses evidence like cell type, habitat, how organisms get food, their structure, and their ancestry.

Domains and Kingdoms

A Closer Look: Are Viruses Living Things?

• Viruses cause diseases like colds, chicken pox, or the flu.
• Viruses have some traits of living things but not all:
  • They are organized and have a structure.
  • They reproduce, but only by taking over living cells.
  • They use energy from the host cell, not on their own.
  • They are not made of cells and do not maintain homeostasis.
  • They do not grow or develop like living things.
• Most scientists say viruses are not living things because they lack several characteristics of life.