Biology Grade 9 Notes

Characteristics of Living Things & Classification of Organisms

In this module, we will cover what makes something living, the classification of organisms, and using dichotomous keys.

Movement:
- An action by an organism or part of an organism causing a change of position or place.
Respiration:
- The chemical reactions that break down nutrient molecules in living cells to release energy for metabolism.
Sensitivity:
- The ability to detect or sense stimuli in the internal or external environment and to make appropriate responses.
Growth:
- A permanent increase in size and dry mass by an increase in cell number or cell size or both.
Reproduction:
- The processes that make more of the same kind of organism.
Excretion:
- The removal from organisms of toxic materials, the waste products of metabolism (chemical reactions in cells including respiration), and substances in excess of requirements.
Nutrition:
- The taking in of materials for energy, growth, and development.
- Plants require light, carbon dioxide, water, and ions.
- Animals need organic compounds, ions, and usually water.

There are millions of species of organisms on Earth.
A species is defined as a group of organisms that can reproduce to produce fertile offspring.
Species can be classified into groups by the features that they share.
- For example, all mammals have bodies covered in hair, feed young from mammary glands, and have external ears (pinnae).

The Binomial System is a classification system with two naming parts.
Organisms were first classified by Linnaeus, a Swedish naturalist.
- Allows the subdivision of living organisms into smaller and more specialized groups.
- The species in these groups have more and more features in common the more subdivided they get.
He named organisms in Latin using the binomial system.
- The scientific name of an organism is made up of two parts:
  - Genus (always given a capital letter)
  - Species (starting with a lower case letter)
- Genus indicates a group of species that are related to one another (e.g., horses and donkeys are in the same genus but different species).
- When typed, binomial names are always in italics (which indicates they are Latin) e.g. Homo sapiens
- When handwritten, the name should be underlined.
The sequence of classification is: Kingdom, Phylum, Class, Order, Family, Genus, Species.

Kingdom Definition: The highest level of classification in which all organisms can be grouped.
- There are generally 6 different types, but you will focus on 5.
- Bacteria and archaea are grouped into prokaryotes.

Keys are used to identify organisms based on a series of questions about their features.
Dichotomous means ‘branching into two’.
- It leads the user through to the name of the organism by giving two descriptions at a time and asking them to choose.
- Each choice leads the user onto another two descriptions.
In order to successfully navigate a key, you need to pick a single organism to start with and follow the statements from the beginning until you find the name.
Then pick another organism and start at the beginning of the key again, repeating until all organisms are named.

Classification systems aim to reflect evolutionary relationships between species.
Traditional biological classification systems grouped organisms based on the features that they shared.
If organisms shared more similar features then they were said to be more closely related.
In the past, scientists encountered many difficulties when trying to determine the evolutionary relationships of species based on this method.
Using the physical features of species (such as color/shape/size) has many limitations and can often lead to the wrong classification of species.

Organisms share features because they originally descend from a common ancestor.
- Example: all mammals have bodies covered in hair, feed young from mammary glands, and have external ears (pinnae).
Originally, organisms were classified using morphology (the overall form and shape of the organism, e.g., whether it had wings or legs) and anatomy (the detailed body structure as determined by dissection).
As technology advanced, microscopes, knowledge of biochemistry and eventually DNA sequencing allowed us to classify organisms using a more scientific approach.
Studies of DNA sequences of different species show that the more similar the base sequences in the DNA of two species, the more closely related those two species are (and the more recent in time their common ancestor is).
This means that the base sequences in a mammal’s DNA are more closely related to all other mammals than to any other vertebrate groups.

The sequences above show that Brachinus armiger and Brachinus hirsutus are more closely related than any other species in the list as their DNA sequences are identical except for the last but one base (B. armiger has a T in that position whereas B. hirsutus has an A).
As DNA base sequences are used to code for amino acid sequences in proteins, the similarities in amino acid sequences can also be used to determine how closely related organisms are.

Main features of all animals:
- Multicellular
- Cells contain a nucleus
- Cells DO NOT HAVE: cell walls or chloroplasts
- They feed on organic substances made by other living things.

Main features of all fungi (e.g., molds, mushrooms, yeast)
- Usually multicellular
- Cells have:
  - Nuclei
  - Cell walls (not made from cellulose)
- Do not photosynthesize but feed by saprophytic (on dead or decaying material) or parasitic (on live material) nutrition
Produce spores: tiny groups of cells with outer covering - helps them to survive harsh conditions
Spores can be carried by wind or on an organism
Spores produce new fungi

Main features of all Protoctists (e.g., Amoeba, Paramecium, Plasmodium)
- Most are unicellular but some are multicellular
- All have a nucleus, some may have cell walls and chloroplasts
- Meaning some protoctists photosynthesise and some feed on organic substances made by other living things

Main features of all Prokaryotes (bacteria, blue-green algae)
- Often unicellular
- Cells have cell walls (not made of cellulose) and cytoplasm but no nucleus or mitochondria