Biology Form 1 Chapter 3

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Biology

Form 1

Chapter 3

LIVING THINGS AND THEIR

ENVIRONMENT I

Website: www.learnmalawi.com

Email: [email protected]

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LIVING THINGS AND THEIR ENVIRONMENT OBJECTIVES

By the end of this chapter, the student should be able to: 1. list the characteristics of living things

2. classify living things

3. identify living things using keys, hierarchy and scientific names

CONTENTS

• Characteristics of living things

o feeding, breathing, excretion, irritability, growth, reproduction and movement

• Classification of living things o habitats

o feeding methods

o similarities and differences • Identification of living things

o discussing a dichotomous key o using a dichotomous key

o constructing dichotomous keys

o sorting organism into various hierarchy (kingdom, phylum, class, order, family, genus and species)

o using scientific names to identify organisms (binomial system) ▪ identifying organisms using local and scientific names

(lion, leopard, cow, dog, mango, maize, housefly, cockroach, bees)

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INTRODUCTION

Organisms are surrounded by both living and non-living things. The surrounding of an organism is called the environment. Organisms are best suited in a natural environment than an artificial environment because there are several interactions, both visible and invisible, that take place between an organism and its environment.

CHARACTERISTICS OF LIVING THINGS

Biology is the study of life. Some characteristics of life distinguish living and nonliving things. To identify whether an item in the environment is living or non-living, seven characteristics are used. These are:

1. Feeding/nutrition - living things take have different wants of obtaining nutrients from the environment. Other living things e.g. plants manufacture food through photosynthesis. Other living things eat get their food by eating other living things e.g. plants and

animals. The food supply nutrients to the organism for energy, growth, and maintenance of the body.

2. Breathing/respiration - Respiration is a chemical reaction that happens within cells to release energy from food. All organisms use this energy for different functions in life.

3. Excretion - living things produce metabolic wastes that result from metabolic reactions. organisms have mechanisms of removing these wastes.

4. Sensitivity/ irritability - all living things can detect or sense stimuli and respond to them.

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5. Growth - All living things grow. organisms start small and get larger through growth of cells or through cell division that produces new cells.

6. Reproduction – living things have the ability to make new organisms of the same species through reproduction. During this process parents pass genetic information onto their offspring. 7. Movement - All living things move in some way. This may be

obvious, such as animals that are able to walk, or less obvious, such as plants that have parts that move to track the movement of the sun.

CLASSIFICATION OF LIVING THINGS

Living may be classified according to the following: • habitats

• feeding methods

• similarities and differences

Classifying organisms using habitats

Most places on Earth can support life. Some organisms live in ‘extreme’ places such as: Sulphur springs, polar regions, deep trenches, upper atmosphere, hot deserts, and inside other organisms. Plants are mainly classified due to their habitats. Most plants may be in the water, or on/in the land. Here are classes of plants according to habitats:

• xerophytes - plants which are able to survive in an environment with little availability of water or moisture.

• hydrophytes - plants which have adapted to living in or on an aquatic environment.

• hygrophytes - plants which grow in a moist habitat.

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Most animals may be classified by feeding behaviour into the following groups:

• Herbivores - feed on plants only • Carnivores - feed on animals only

• Omnivores - feed on both animals and plants

Classifying organisms using similarities and differences

Living organisms can also be classified according to their similarities and differences. Carolus Linnaeus classified living organisms based on the similarities and the differences of the body structures of living organisms. According to Carolus Linnaeus, living organisms can be divided into two main groups: the kingdom of plants and the kingdom of animals. This system is hierarchical divided into highest levels and lowest levels. Each level is called a taxon. A taxon is composed starting from the group with the most common characteristics (the highest taxon) to the group with the most specific characteristics (the lowest taxon). The taxonomic rank for plants and animals from the highest to the lowest level can be seen in diagram below:

So, the higher group means more different in characteristics and it has more members. The lower group means more similar in characteristics and it has less member.

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Whittaker classification

Linnaeus classification used morphology/structure to classify organisms. However, under whittaker, the following organisms characteristics were used:

1. complexity of cell structure

a. Cell type- prokaryotic or eukaryotic. b. Cell wall

c. Nuclear membrane 2. Mode of nutrition

3. Body organization

4. Phylogenetic or evolutionary relationship

According to whittaker, living organisms can be classified into five

kingdoms. These are: Monera, Protista, fungus, plantae, and animalia. In general, monera and Protista are unicellular while fungi, plantae and

animalia are multicellular.

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Five Kingdoms

Char acter

Monera Protista Fungi Plantae Anima

lia Cell

Type

prokaryotic eukaryo

tic

eukaryotic eukaryotic eukar

yotic Cell

wall Noncellulosic(polysaccharid e + amino acid)

Present

in some Present without cellulose Present with cellullose Absent Nucle

ar mem brane

Absent Present Present Present Prese

nt Body

organ izatio n

cellular cellular Multicellular/

loose tissue Tissue / organ Tissue / organ /orga n syste m Mode of nutriti on Autotrophic(c hemo-/photo- synthetic) and heterotrophic (saprophytic/ parasitic) Autotro phic (photos ynthetic ) and heterot rophic Heterotrophic(sa prophytic/parasiti c) Autotrophic( photosynthet ic) Heter otroph ic (holoz oic, sapro phytic , etc) Evolu tion perio d Early-middle

precambrian Late precam

brian - early

phanerozoic phanerozoic phane

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Copyright © learnmalawi | All rights reserved paleozo ic Exam ples Bacteria, blue green algae. Mycelial bacteria, gliding bacteria All protozo a, eukaryo tic algae, slime molds Conjugation fungi, sac fungi, club fungi, yeast

All green plants above green algae All animal s develo ping from blastul us

VIRUSES, VIROIDS AND LICHENS

In the five- kingdom classification of Whittaker there is no mention of some acellular organisms like viruses and viroids, and lichens

Viruses are not part of whittaker classification because they are not truly ‘living’ – no cell structure, but just exist until they get inside a living cell. The viruses are non-cellular organisms that are characterised by having an inert crystalline structure outside the living cell (or host cell). Once they infect a cell they take over the machinery of the host cell to replicate themselves, killing the host.

Viruses are largely proteins but in addition viruses also contain genetic material, that could be either RNA or DNA. No virus contains both RNA and DNA. A virus is a nucleoprotein and the genetic material is infectious. In general, viruses that infect plants have single stranded RNA and viruses that infect animals have either single or double stranded RNA or double stranded DNA. Bacterial viruses or bacteriophages (viruses that infect the bacteria) are usually double stranded DNA viruses.

Viruses cause diseases like mumps, small pox, herpes and influenza. AIDS in humans is also caused by a virus.

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Viroids: this is also an infectious agent that is smaller than viruses. It is a

free RNA; it lacks the protein coat that is found in viruses, hence the name viroid.

Lichens : Lichens are symbiotic associations i.e. mutually useful

associations, between algae and fungi. The algal component is known as

phycobiont and fungal component as mycobiont, which are autotrophic

and heterotrophic, respectively. Algae prepare food for fungi and fungi provide shelter and absorb mineral nutrients and water for its partner. So close is their association that if one saw a lichen in nature one would never imagine that they had two different organisms within them. Lichens are very good pollution indicators – they do not grow in polluted areas.

IDENTIFICATION OF LIVING THINGS

Living organisms are identified by a dichotomous key

Dichotomous key

A dichotomous key is a tool (chart or set of instructions) that allows the user to determine the identity of unknown organisms. Unknown

organisms are identified by comparison with existing description of organisms. Keys consist of a series of choices that lead the user to the correct name of a given item. "Dichotomous" means "divided into two parts". It is called dichotomous key because at each step there are two choices such that an organism can either be in the group or not. With the key, the following should be noted:

• With each sequential division, more information is revealed about the

specific features of a particular organism

• When the organism no longer shares its totality of selected

characteristics with any organism, it has been identified

• When using a dichotomous key to identify specimens it is preferable

to use immutable features (i.e. features that do not change)

o Size, colouration and behavioural patterns may all vary

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o Physical structures (e.g number of limbs) and biological

processes (e.g. reproduction methods) make for better characteristics

A dichotomous key can either be a chart or a set of instructions. Question

Given the following plants (figure x.x) construct

Figure x.x: unknown plants to be identified a. Dichotomous key chart

b. Dichotomous key go to instructions solution

a. Figure x.x is an example of a dichotomous key chart which is called a spider key

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b. Figure x.x is an example of a dichotomous key which is a set of Go to instructions

Constructing dichotomous keys

Below we have listed the steps you need to follow when creating a dichotomous key.

Step 1: List down the characteristics

Pay attention to the specimens you are trying to identify with your dichotomous key. List down the characteristics that you can notice. For example, say you are trying to classify a group of animals. You may notice

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that some have feathers whereas others have legs, or some have long tails and others don’t.

Step 2: Organize the characteristics in order

When creating your dichotomous key, you need to start with the most general characteristics first, before moving to the more specific ones. So it helps to have identified the more obvious and less obvious contrasting characteristics among the specimen before creating your dichotomous key.

Step 3: Divide the specimens

You can use statements (i.e. has feathers and no feathers) or questions (does it have feathers?) to divide your specimens into two groups. The first differentiation should be made on the most general characteristic.

Step 4: Divide the specimen even further

Based on the next contrasting characteristic, divide the specimen further. For example, first, you may have grouped your animals as have feathers and have no feathers, in which case the ones with feathers can be

categorized as birds while you can further subdivide the ones that have no feathers as having fur and having no fur. Continue to subdivide your

specimen by asking enough questions until you have identified and named all of them.

Step 5: Draw a dichotomous key diagram

You can either create a text-based dichotomous key or a graphical one where you can even use images of the specimen you are trying to identify. Here you can use a tree diagram or a flowchart as in the examples below.

Step 6: Test it out

Once you have completed your dichotomous key, test it out to see if it works. Focus on the specimen you are trying to identify and go through the questions in your dichotomous tree to see if you get it identified at the

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end. If you think the questions in your dichotomous key needs to be rearranged, make the necessary adjustments.

Question

Make Dichotomous Key for insects

Solution

Sorting organism into various hierarchy

When sorting organisms kingdom is always ranked the highest followed by division, class, order, family, genus, and species.

The kingdom is the highest level of classification, which is divided into subgroups at various levels. There are 5 kingdoms in which the living

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organisms are classified, namely, Animalia, Plantae, Fungi, Protista, and Monera.

phylum the next level of classification and is more specific than the

kingdom. There are 35 phyla in kingdom Animalia. For Example – Porifera, Chordata, Arthropoda, etc.

Class is more specific than phyla. Kingdom Animalia includes 108 classes

including class mammalia, reptilia, aves, etc

Order is a more specific rank than class. The order constitutes one or

more than one similar families. There are around 26 orders in class mammalia such as primates, carnivora, etc.

Family - This category of taxonomic hierarchy includes various genera that

share a few similarities. For eg., the families in the order Carnivora include Canidae, Felidae, Ursidae, etc.

A group of similar species forms a genus. Some genera have only one species and is known as monotypic, whereas, some have more than one species and is known as polytypic. For eg., lion and tiger are placed under the genus Panthera.

Species

It is the lowest level of taxonomic hierarchy. There are about 8.7 million different species on earth. It refers to a group of organisms that are similar in shape, form, reproductive features. Species can be further divided into sub-species.

Examples of Taxonomic Hierarchy

Following are some of the examples of taxonomic hierarchy:

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organisms are named by placing them in a hierarchical structure, each level being given a name (e.g., kingdom, division (phylum), class, order, family, genus, species). Taxonomic units at a given level are termed taxa (singular taxon).

Uninominal naming system

Names of higher order taxa (e.g., kingdom, phylum, class, order, family, genus) are uninominal (i.e., each name is a single word).

Binomial naming system

Names of species are binomial which means two names make one name (e.g., Magnolia virginiana). The names are given in Latin. The first name is the name of the genus where the organism belongs. The first name starts with a capital letter. The second name in the name of its species and is given in lower case (small letters).

Other naming systems

names of taxa below the rank of species (e.g., subspecies, varieties) are comprised of three or more words (e.g., Panicum virgatum var. cubense)

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