Living and Non-Living Things

Living things

Living things exist and are alive. They are made of microscopic structures called cells. They grow and exhibit movement or locomotion. They carry out metabolism, which includes anabolic and catabolic reactions.

Living things also has the ability to reproduce i.e produce a new life of their own kind through procreation. Living things have a particular life span and are not immortal.

Following are the important characteristics of living things:

1. All living things have life. They eat, breathe, feel, grow, and reproduce. 

2. They carry out chemical reactions within their body, which generates energy. This energy within the body is then used to carry out various activities. 

3. Imagine, what would happen without energy being generated inside the body of a living thing. The living thing’s capability to perform various tasks will end and the living being will cease to exist. 

4. Most often, living things also show the capability to move which is called locomotion. 

5. Every living thing that has life, shows the presence of the cell. Inside the cells, there are chemicals that carry out various chemical reactions. These chemical reactions lead to a number of processes. 

6. There are unicellular organisms- living organisms with single cells and multicellular organisms- living organisms with multiple cells living on earth. 

7. Multicellular organisms also possess tissues, organs, and organ systems, and thus, such organisms have various cells to carry out various functions.

Non Living things

Non-living things are not alive. They do not possess life. They do not have cells and do not grow or show locomotion/movement. They do not undergo metabolism with anabolic and catabolic reactions. They do not reproduce.

Non-living things do not have a life span. They do not respire as they do not require food for energy and hence do not excrete. They do not fall into any cycle of birth, growth or death. They are created and destroyed by external forces.

Examples of non-living things include stone, pen, book, cycle, bottle, etc.

Characteristics Of Non-living Things

The important characteristics of non-living things are mentioned below:

1. Non-living things are lifeless. They do not have cells, and there is no protoplasm which forms the basis for life to exist.

2. Lack of protoplasm leads means no metabolic activities.

3. They do not have a definite and certain size of their own. They take the shape of the substance they are contained in, for example, a liquid takes the shape of its container. Stones, rocks and boulders are moulded by the changing environment and landscape. The change in the state of a non-living thing is due to an external influence.

4. Non-living things “grow” by accretion. It occurs through adding materials externally. For example, A snowball may increase in size due to the accumulation of smaller units of its own to its outer surface.

5. Non-living things never die as they do not have cells with a definite lifespan. Immortality is a distinguishing factor.

6. Fundamental life processes such as reproduction, nutrition, excretion, etc. are absent in non-living things.

Classification of living things

There are millions of types of organisms on the earth and memorizing each of them separately is impossible. So, they are classified into different groups based on similarities and differences. This classification has further sub-groups. These are classified in the taxonomic hierarchy.

The taxonomic hierarchy from the largest to the smallest is:
1. Domain
2. Kingdom
3. Phylum/division
4. Class
5. Order
6. Family
7. Genus
8. Species

The three domains are:
1. Domain Bacteria
2. Domain Archaea
3. Domain Eukarya

Five-kingdom classification by R.H Whittaker (1969):

The domain Bacteria and Archae are placed in one kingdom known as kingdom  Monera. The Domain Eukarya is divided into four kingdoms. So, all the living organisms are classified into five kingdoms that are:
1. Monera
2. Protista
3. Fungi
4. Plantae
5. Animalia

Monera

This kingdom includes the unicellular eukaryotes, that is, the bacteria and archaea.

The sub-kingdoms are Archaebacteria and Eubacteria.
Characteristics:
1. These are prokaryotes hence, lack nucleus and cell organelles. Only DNA is present in them.
2. These reproduce by binary fission.
3. Some of these have structures that help in adhesion known as pili, while some have structures for the movement known as flagella.
4. These synthesise their food either by using sunlight (photoautotrophs) or by using chemicals (chemoautotrophs).
5. These show quick reproduction as these do not reproduce sexually that is by the formation of gametes.

Archaebacteria-
These are the ancient bacteria that are adapted to survive in the harsh conditions of the environment, and so are known as extremophiles. Unlike eubacteria, they do not have peptidoglycan in their cell wall. Instead, it is formed of pseudomuerin.

Based on the conditions they can survive in, they are divided into different groups:
1. Methanogens- These are anaerobic bacteria that produce methane as a byproduct by their metabolism. Example: Methanobacillus.
2. Halophiles- These are the archaebacteria that live in extremely salty conditions. Example: Halobacteria
3. Thermoacidophiles- These are the archaebacteria that can survive in extremely hot and acidic conditions. Example: Thermoplasma

Eubacteria-
These are the true bacteria that are different from archaebacteria in two features:
1. They have peptidoglycan in their cell wall
2. They cannot survive in extreme conditions
The eubacteria include both autotrophic and heterotrophic bacteria.

Some of these can also reproduce sexually by conjugation.
These are divided into five phyla:
1. Chlamydias- These are parasitic and survive in animal cells only. Example: Chlamydia trachomatis.
2. Cyanobacteria- These are photoautotrophs and gram-negative bacteria. These are also known as blue-green algae. These are plant-like as are green in colour. Example: Nostoc and Anabaena.
3. Proteobacteria- These are gram-negative bacteria and include pathogenic bacteria like Helicobacter pylori.
4. Spirochaetes- These are gram-negative and heterotrophic bacteria. These are helical in shape. Example: Treponema pallidum.
5. Gram-positive bacteria- These bacteria retain the gram stain due to the presence of a thick peptidoglycan layer in their cell wall. Example: Actinomyces, Staphylococcus and Streptococcus.

Gram staining technique:

Gram-positive and Gram-negative bacteria are differentiated by a staining technique known as Gram staining.
1. The bacterial cells are heat-fixed on the slides and covered with a coverslip.
2. It is stained with crystal violet stain for 30 seconds that gives the cells a purple colour.
3. Iodine is used as a mordant to fix the crystal violet stain in the cells. It is used for 1 minute.
4. It is washed with 95% ethanol to decolourise it for 10 seconds. The crystal violet stain from the Gram-negative bacteria gets washed off.
5. The slide is stained with safranin for 30-60 seconds. This gives the Gram-negative bacteria a pink colour.
6. Rinse the slide with distilled water.
7. When you visualise this under the microscope, the Gram-positive cells appear purple while the Gram-negative cells appear pink (Fig.5).

Protists

As seen in the previous part, these are unicellular eukaryotic organisms. Some of them are multicellular too. Some of them are photoautotrophs, while some are heterotrophs.

This kingdom includes:
1. Protozoa, that is simple animals.
2. Algae, that is plant-like

Most of them reproduce asexually, while some can reproduce sexually by producing gametes.

The protists can be classified into various phyla:
1. Rhizopoda- These have false-feet like structures known as pseudopods extending from the protoplasm. These are also known as amoeboids. Example: Amoeba (Fig 6b).
2. Actinopoda- These have false-feet like structures known as pseudopods too, but these are needle-like. Example: Radiolarians.
3. Foraminifera- These have protoplasmic extensions like pseudopods to help in the locomotion and also, have rigid shells. Example: Forams.
4.  Pyrrhophyta- These are dinoflagellates and have chlorophyll pigments and two flagella to help in locomotion. These are mostly found in marine water. Example: Red tides.
5. Euglenophyta- These are euglenoids and have two flagella at their anterior end and are commonly found in freshwater. These have chlorophyll pigments. Example: Euglena (Fig 6c).
6. Chrysophyta- These include the diatoms, yellow-green algae and golden-brown algae that are found more in freshwater. The golden algae have Fucoxanthin that gives them a golden colour. The yellow-green algae lack Fucoxanthin and have beta-carotene. Example: Chrysosaccus and Melosire.
7. Rhodophyta- These are the red algae that have pigment phycoerythrin. They are found more in freshwater. Example: Red seaweed.
8. Phaeophyta- These are brown algae and are found more in marine water. Example: Kelp.
9. Chlorophyta- These are green in colour due to the abundant presence of chlorophyll pigments. Example: Chlamydomonas and green seaweed.

Fungi

These are heterotrophic organisms that absorb nutrients from their food sources and do not engulf the food like animals. Some of them are multicellular like filaments, while some are unicellular. The tiny filaments in the fungi are known as hyphae that have cell walls made up of chitin. These hyphae are divided into separate cells by septa through which molecules and even organelles can pass. Some of these do not have septa and are known as coenocytic. Some of these are decomposers. Some are parasites while some are mutualists. Mass of branching or interwoven hyphae in the fungi is known as mycelium. These can reproduce by sexual and asexual reproduction. Spores are produced to help in reproduction in both methods. Spores are dispersed and give rise to new mycelium.

Fungi are divided into five phyla:

1. Chytridiomycota- These are the most primitive and simplest true fungi. Most of these are unicellular, while some multicellular fungi are coenocytic. These reproduce by producing flagellated gametes. These also reproduce by producing diploid zoospores asexually which develop to form a new organism. Most of them are present in aquatic habitat.

Remember: Both male and female gametes are flagellated in phylum Chytridiomycota.

2. Zygomycota- These are coenocytic and reproduce asexually in normal conditions by producing haploid spores. In unfavourable conditions, they divide sexually by conjugation. Mycelium with opposite mating strains (+ and -) come and fuse to form zygosporangium by plasmogamy (fusion of cytoplasm). Then karyogamy (fusion of nucleus) occurs. When the conditions become favourable, meiosis takes place in them to produce haploid spores that develop into new organisms. Some of these live on food such as bread and sweet potatoes, while others are symbionts. Example: bread moulds (Rhizopus stolonifer) (Fig. 7 and Fig 8).

Plantae

This kingdom includes vascular and non-vascular plants. Vascular plants are of two types: seedless and seed plants.

Alternation of generations is seen in sexually reproducing organism as they have haploid and diploid stages in their life. The seedless plants have sporangia in which spores are present. Gametangia are the structure in which gametes are produced. Sporophytes undergo sexual reproduction while gametophytes reproduce asexually.

This kingdom has five divisions:

1. Thallophya
2. Bryophyta
3. Pteridophyta
4. Gymnosperms
5. Angiosperm

Thallophyta:
These are autotrophic organisms and are non-vascular plants. These do not have a well-differentiated body like plants. Most of them are aquatic. Their cells have a cell wall formed of cellulose. Some of them are filamentous. Some have flat thallus like structure, while others are unicellular. These are flowerless plants.
These can reproduce asexually either by fragmentation or by producing spores. These can reproduce sexually by producing gametes. Example: Spirogyra, Volvox and Chlamydomonas.

Bryophyta:

These are the earliest terrestrial plants. These are non-vascular plants. These are considered as “amphibians of the plant kingdom” because though these are terrestrial but water is necessary for fertilisation while sexual reproduction. These have thallus i.e. leaf-like green structures. These have root-like structures known as rhizoids. The dominant stage of their life cycle is the haploid gametophyte.

Sexual reproduction: The spores are dispersed which result in the formation of protonema. Bud-like structures known as gametophores are produced on protonema under favourable conditions. Protonema and gametophores are together known as a gametophyte. The gametophyte has gametangia of two types: archegonia (female gametangia) and antheridia (male gametangia). Sometimes these are present on the same gametophyte (bisexual), while sometimes on different gametophytes. Archegonia produces egg while antheridia produce sperm. The sperm moves through the water to reach the archegonium to fertilise with egg. Zygote and embryo are formed inside the archegonium. An embryo develops into the sporophyte. It then matures and produces sperms and cycle continues again.

Sporophytes of bryophytes have foot, a seta and a capsule. The foot is embedded into the archegonium to acquire nutrition from the gametophyte. Capsule or the sporangium produces spores and is connected to the foot by seta.

 These are divided into three subphyla:

a. Liverworts- These have pores to allow movement of water and gases. These have structures known as elaters that help in spore dispersal. These can also reproduce asexually by breaking small branches known as gemmae that can develop into a new plant. Example: Marchantia

b. Hornworts- These are pipe-like in structure and have stomata to help in exchange of gases and water. Many of them live in a symbiotic relationship with cyanobacteria. These have pseudoelaters to help in spore dispersal. These do not have seta in their sporophytes. Example: Ceratophyllum demersum.

c. Mosses- Many of the non-vascular plants are mosses. The gametophytes have true-leaf like structures but do not have stomata. Stomata are found only on sporophytes. These have teeth-like structures known as peristome on the mouth of sporangia that open and closes to help in spore dispersal. Example: Polytrichum.

Pteridophyta:

These are seedless, vascular and flowerless plants. Unlike bryophytes, the sporophytes are the dominant stage in them. These have xylem and phloem to help in the transport of substances. These had microphylls which are small leaves. These have sporophylls in which the sporangia are present. Most of them were homosporous, that is, produce one type of spore while some were heterosporous that produces two types of spores known as megaspores and microspores. The megaspores are produced from megasporangia present in megasporophyll. The microspores are produced by microsporangia present in microsporophyll. 

These are divided into two subphyla:

1. Lycophyta- These grow on tall trees. These include club mosses, quillworts and spike mosses. The quillworts and spike mosses are heterosporous while club mosses are homosporous. Gametophytes of some lycophytes such as Lycopodium produce independent gametophyte that lives in a symbiotic relationship with plant roots away from the sporophyte or on the ground. The sporangia are present in a cone-like structure known as strobili. Strobili are formed of sporophylls.
2. Monilophyta- This includes ferns, horsetails and whisk ferns.
a. Ferns- These have large leaves known as fronds that originate from horizontal stems. Most of them are homosporous. These have megasporophylls.
b. Horsetails- These have brushy stems like tails of horses. These have small leaves, but the green stem is the main site for photosynthesis. These are homosporous that form bisexual gametophytes. c. Whisk ferns- These have stems but no roots and leaves so are known as whisk ferns. These have three fused sporangia on the stem that appears like a yellow knob. These are homosporous and give rise to bisexual gametophytes.

Gymnosperms:

These are vascular plants with naked-seeds that are not enclosed in chambers like in angiosperms. Most of them are known as conifers as these are cone-bearing plants. Cones are scaled structures in which reproductive organs are present. Examples: Pines and Redwoods.These have naked seeds as these are not enclosed in the ovary and are partially enclosed in sporophylls or strobilus (cone-like arrangement of sporophylls).

These can be monoecious (bisexual) or dioecious (unisexual) depending on the presence of male and female sporangia on the plant.

Sexual reproduction in Conifers:
These are dioecious. In the pollen cone, microsporangia or male sporangia are present. In it, microsporophytes are present which divide by meiosis to form microspores. These develop into pollens. In the ovulate cone, the female sporangia or megasporangia is present that has two ovules. When the pollen grain moves to reach the ovule, it germinates to form pollen tube. The megasporocyte divides by meiosis to form 4 haploid cells and one of them forms a megaspore. The megaspore develops to form female gametophyte that has archegonia which produce an egg. When the egg is formed, the sperm reaches it and fertilise. Fertilisation occurs one year after pollination. The zygote develops to form the embryo, and the ovule forms the seed that encloses the embryo and provides nutrition to it. It then develops to form a sporophyte .

Gymnosperms are divided into four subphyla:

1. Coniferophyta- It is the phylum with maximum varieties of gymnosperms. These are also known as conifers. These are tall and have needle-like leaves with a thick cuticle. This prevents excessive water loss. These do not have vessel elements. Examples: Pines and Cedars.
2. Cycadophyta- These have large strobili or cones in the leaves. These are also known as Cycads. Example: Encephalartos ferox (Fig 6).
3. Ginkgophyta- It includes only one species known as Ginkgo biloba. It has unique fan-shaped leaves. These are monoecious. Female seeds have a bad smell of rancid butter.
4. Gnetophyta- This includes Ephedra, Gnetum, and Welwitschia. These have vessel elements like angiosperms, but have similarities to conifers.

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