BIO101 Lecture Notes - Characteristics & Classification of Living Organisms PDF

BIO 101 Characteristics and Classification of Living Organisms  Welcome to the exciting and amazing world of living things.  Go outside and look around you. Look at the sky, the soil, trees, plants, people, animals.  Nature is all around you if you have the eyes to see it. Count how many livin...

BIO 101 Characteristics and Classification of Living Organisms  Welcome to the exciting and amazing world of living things.  Go outside and look around you. Look at the sky, the soil, trees, plants, people, animals.  Nature is all around you if you have the eyes to see it. Count how many living things you can see.  What is it that makes living things different from things that are not alive?  Biology is the study of living things. It deals with what all living things can do, how they do it and why they do it. In biology, there is always a relationship between the structure of an organism, its function, and its adaptation to its function or environment.  Biology also tackles the important topics such as population, environmental issues as well as health issues.  When you have studied this unit, you should be able to:  list and describe the characteristics of organisms  define the terms nutrition, excretion, respiration, sensitivity, reproduction, growth and movement  outline the use of a hierarchical classification system for living organisms  classify living organisms into kingdoms, orders, classes, families, genera and species  define and describe the binomial system of naming species  construct dichotomous keys  use simple dichotomous keys based on easily identifiable features. Characteristics of Living Things  There are seven (7) activities which make organisms different from non-living things. These are the seven characteristics of living organisms.  Nutrition/ Feeding  Living things take in materials from their surroundings that they use for growth or to provide energy. Nutrition is the process by which organisms obtain energy and raw materials from nutrients such as proteins, carbohydrates and fats.  Plants, algae, and some bacteria harvest the energy of sunlight through photosynthesis, converting radiant energy into chemical energy.  These organisms, along with a few others that use chemical energy in a similar way, are called autotrophs (“self-feeders”).  All other organisms live on the organic compounds autotrophs produce, using them as food, and are called heterotrophs (“fed by others”).  At least 95% of the kinds of organisms on Earth—all animals and fungi, and most protists and prokaryotes—are heterotrophs.  Respiration  Respiration is the release of energy from food substances in all living cells.  Living things break down food within their cells to release energy for carrying out the following processes.  Cellular respiration is the complete oxidation of organic compounds such as glucose to extract energy from chemical bonds. 1  Anaerobic respiration:  In animals  Most organisms cannot respire without oxygen. But some organisms and tissues can continue to respire if the oxygen runs out.  These organisms and tissues use the process of anaerobic respiration.  Animal muscles can respire anaerobically for short periods of time - even though the process is relatively inefficient, it's better to continue respiring and be able to run away from danger - or run a race.  The glucose in muscle is converted to lactic acid:  Glucose → Lactic acid (+ energy released)  In general, anaerobic respiration consists of two main basic steps: Glycolysis: the break down of glucose into two pyruvate, two ATP, and two NADH (an electron carrier) molecules.  Fermentation: the production of alcohol or lactic acid substrates and NAD+ for energy production  Movement  All living things move. It is very obvious that a leopard moves but what about the thorn tree it sits in?  For example, different types of locomotory organs are found in protozoans. They may bear flagella (flagellates), cilia (ciliates) pseudopodia (sarcodines).  Locomotory organs are absent in the parasitic forms (Sporozoa).  Excretion  All living things excrete. As a result of the many chemical reactions occurring in cells, they have to get rid of waste products which might poison the cells.  Excretion is an essential process through which body gets rid of metabolic wastes and maintains osmotic pressure.  Several waste products such as water, carbon dioxide and nitrogenous substances are generated during cellular activities. These products are harmful to the body if accumulated and therefore need to be removed. In mammals, specialized organ called kidney eliminates most of the water and nitrogenous substances from the body.  Excretion is defined as the removal of toxic materials, the waste products of metabolism and substances in excess from the body of an organism.  In majority of vertebrates, the chief excretory organ is the kidney.  Growth  Growth is seen in all living things. It involves using food to produce new cells.  It is the permanent increase in cell number and size is called growth.  Reproduction  All living organisms have the ability to produce offspring.  Reproduction is the biological process by which new organisms are created from their parents. There are two main types of reproduction:  Asexual reproduction  A single organism reproduces without the involvement of another organism. The offspring is genetically identical to the parent.  Sexual reproduction 2  A male and female organism combine their genetic information to create a new organism that is genetically unique.  In humans, reproduction involves the following steps:  Gamete production: The male gamete (sperm) and the female gamete (egg) are produced.  Fertilization: The sperm fertilizes the egg in the female's reproductive system.  Zygote formation: The fertilized egg, now called a zygote, develops into an embryo and then a fetus.  Sensitivity  All living things are able to sense and respond to stimuli around them such as light, temperature, water, gravity and chemical substances.  These seven characteristics of living organisms form the basis of the study of Biology.  Whilst many other things carry out one or more of the above processes, only living organisms possess all of these characteristics. CLASSIFICATION OF ANIMALS  When the librarian has a new book to add to the library, he or she will group it with books on a similar to.  Classification can be defined as grouping organisms according to their structural similarities.  This means that organisms that share similar features are placed in one group. These groups are arranged from the largest group of organisms to the smallest group of organisms.  The groups, from largest to smallest, are arranged as follows: kingdom, phylum (plural phyla), class, order, family, genus (plural genera) and species.  The species is the smallest group of organisms.  As you go through the classification hierarchy, you will see that scientists have used broader features to put organisms into kingdoms, which are the largest groups of organisms.  When you move down towards the species, which are the smallest groups of organisms, features are becoming specific.  In other words, two organisms that belong to the same species share more features than those in the same kingdom but in different species.  A species can be defined as a group of organisms with similar features, and these organisms are capable of breeding and produce fertile offspring.  Classification hierarchy has many uses.  First, it helps scientists to sort organisms in order.  Second, it helps them to identify new organisms by finding out which group they fit.  Third, it is easier to study organisms when they have been properly identified and correctly named.  Two major classification types are known, 3  Artificial and Natural classifications.  Artificial classification groups the animals for the purpose of convenience, using few and easily observed characters.  Most often these characters are imposed on the organisms hence do not reflect phylogenic and evolutionary relationships. Example of such characters include where the animal lives, how they move, what they feed on, etc.  Natural classification, on the other hand, groups the animals according to their natural affinities, using numerous internal and external characters and even characters waiting to be discovered. They therefore express natural relationships like phylogenic and evolutionary relationships.  Natural classification is preferable and has been adopted in Biology because it allows biologists to see the organismal world as having a unique number of groups with historical and evolutionary relationship.  It introduces a set of classification principles involving  (i) the arrangement of animals in a hierarchical order,  (ii) the arrangement of animals based on structural and natural relationships (homology) and (iii) an arrangement transcending human interpretation and judgment. The Linnaean classification is a fine example of this.  Taxonomy is the branch of biology that is involved in identification, naming and classifying living organisms.  Taxonomy is the science of naming and classifying and organizing organisms in a universally accepted structure.  Taxonomy is a study of the principle, practice and rules of classification and nomenclature of living organisms  There are two bases for such classification.  (1). Phenetic taxonomy, which involves grouping on the basis of phenotypic similarity and engaging complex statistical techniques to obtain a measure of similarity. Characters used are largely morphological, anatomical, biochemical and cytological.  (2). Phyletic taxonomy, which involves grouping on the basis of presumed evolutionary and genetic relationships. The outcomes of the two systems are usually fairly similar despite the fact that phyletic classification is liable to subjective bias.  A species forms the basic unit of classification of animals. There are different ways of distinguishing a species.  This form of organization is usually arranged hierarchically from the largest inclusive grouping to the more specific one.  This is known as the taxonomic rank. This hierarchical taxonomic model (also referred to as Linnaean system) was invented by Carl Linnaeus, a Swedish zoologist, botanist and physician.  Systematics is the process of placing organisms into groups or taxa based on certain relationships between them.  The main categories of classification of living things are- kingdom, division (plants) or phylum (animals), class, order, family, genus and species. 4   Zoologists have had an uneasy time naming and deciding on how animals can be classified. This has necessitated a study in Biology known as Taxonomy (Gk. Taxis, arrangement; nomy, science of), which is concerned with identifying and naming organisms.  You can now imagine what it will be like to identify, name and classify the estimated 3 to 20 million species of animals living on earth and the confusion that will come with it. It is no doubt a daunting task.  Although taxonomy is as old as man himself, the early man attempted taxonomy using personal and practical criteria, hence could not make a tangible headway.  Brief History of Taxonomy Aristotle (300 BC), the famous Greek philosopher and biologist, was the first individual to take serious interest in taxonomy on the basis of structural similarities. He divided living things into 14 groups and went ahead to subdivide these according to size. John Ray (1627-1705), a British naturalist later in the 17th century, also expressed his belief that organisms should have a set of names and advocated for a taxonomic system with natural affinities. Carl von Linné or Carolus Von Linnaeus (1707-1778), a Swedish botanist in the 18th century following the same line of thinking, using plants, wrote a book titled “Systema naturae” in 1758. He named about 12,000 species of plants and animals and classified, and today his scheme is the most acceptable taxonomic scheme the world over.  R. H. Whittaker in 1969 suggested that living things be classified into 5 kingdoms- Monera, Protista, Fungi, Plantae and Animalia.  Zoologists generally belief that classifying animals reduce the enormity of variety of organisms to a sizeable number of groups and therefore assist in overcoming the chaos and confusion involved.  Bacteria, Archaea and Eukarya.  Under each domain is another large category called “Kingdom”, followed by other categories of increasing specificity.  Scientists generally refer to an organism only by its genus and species, which is its two- word scientific name, in what is called binomial nomenclature  Both the Bacteria and Archae are single-celled, prokaryotic, and microscopic. Bacteria are considered true bacteria, and also include photosynthetic cyanobacteria.  Many archaea are extremophiles, which thrive in harsh environments. Examples of Archaea Kingdom  Eukarya are single or multicellular and have eukaryotic cells.  Thermophiles: These are heat-loving archaea found in hot environments, such as hot springs and hydrothermal vents. An example is Pyrolobus fumarii, which holds the record for surviving at the highest known temperature: 113°C!  Halophiles: These are salt-loving archaea. Halobacterium salinarum is a common example that flourishes in the Great Salt Lake and the Dead Sea, where salt concentrations are extremely high.  Methanogens: These archaea produce methane and are found in places such as swamps, marshes, and the intestines of mammals (including humans!). Methanobrevibacter smithii, for example, helps in the digestion of complex sugars in our gut. 5  Linnaeus belief that a species has its own distinctive structural features that it does not share with members of similar but different species (Typological concept).  This may, however, be misleading, as it is a well-known fact that male and female or adult and juvenile forms of the same species may differ structurally. The Biological definition of a species recognizes that it distinctive characters are passed from parents to the offsprings (Biological concept).  A species is therefore described as a group in which members interbreed and share the same gene pool.  The shortfall of the biological definition includes the fact that it is not directly applicable to asexually reproducing individuals and even where applicable they are not always reproductively isolated, as the variant types tends to interbreed where their populations overlap. Some distinct species interbreed occasionally resulting in infertile individuals. To clear these fallouts, an acceptable definition has been developed to accommodate the two views.  A species is a group of individual animals which in the sum total of their characters (morphological, physiological, embryological, genetic etc.) constantly resemble each other to a greater degree than members of other groups; which forms true interbreeding assemblage but will not, under natural conditions, produce viable or fertile offsprings with members of another group.  Animals are placed in Taxa (Gk. Taxis, arrangement), i.e. group of animals that fill a particular category of classification. Each group, called a Taxon, contains animals sharing basic features hence having common ancestry.  Seven major Taxonomic ranks are recognized, i.e. species, genus, family, order, class, phylum and kingdom, listed in ascending order.  The species is the most exclusive group containing fewest animals. There are several species within a genus, several genera within a family, several families within an order and so on.  The higher taxa are therefore more inclusive thus showing hierarchy, e.g. the Human classification shown in Table 1.  Table 1: Taxonomic classification of human beings and their characteristics Taxon Characters kingdom Animalia Multicellular organisms with eukaryotic cells; Cells lack cell walls and chlorophyll; Posses internal cavity for digestion. phylum Chordata Have dorsal nerve chord; Notochord and pharyngeal pouches class Mammalia Warm-blooded vertebrates; Have mammary glands; Body covered with hairs. order Primates Good brain development, Have opposable thumb; Lack claws; scales; horns and hoofs. family Hominidae Stand upright; Limb anatomy supports upright posture; Bipedal locomotion 6  genus Homo Brain maximally developed; Hand anatomy suitable for making tools species sapiens Speech center of brain well developed. This method of classification is analogous to the postal address of a Nigerian as shown in Table 2, which enables his location with some ease among 130 million Nigerians. Table 2: The postal address of a Nigerian as compared with the taxonomic classification of some representative animals Taxon A lion Leopar housefly mosqui Nigerian d to Country Nigeria Animali Animal Animali Animalia kingdom a ia a State Kwara Chordat Chordat Arthrop Arthrop phylum a a oda oda Town Ilorin Mammal Mamm Insecta Insecta class ia alia Compou Staff Carnivor Carnivo Diptera Diptera nd Quarters a ra order House No. 43 Felidae Felidae Muscida Culicid family e ae Surname Yoloye Panthera Panthera Musca Anophe genus les First Victor leo Pardus domestic gambia Name a e species Each of the seven taxonomic ranks can be further divided into three additional categories, i.e. Super-, sub- and infra. Consequently, there are more than thirty categories or taxa. By convention, the following guidelines are followed: -  Names of taxonomic ranks should take lower case initial letters e.g. class Arthropoda.  The Latin forms of all taxon names except the specific name take an initial upper case letter but their anglicized version do not e.g. ‘ the Arthropoda….’; ‘the arthropods…’.  The names of the higher taxa are all pluralized and should be so used in sentences, e.g. ‘the Arthropoda are…’, while the singular of the anglicized version is used for a single member of the taxon e.g. ‘an arthropod is…’. Right from Aristotle’s time to the early 19th century, it was traditional to assign every living organism to two kingdoms, i.e. Plants and animal. This however created some problems for unicellular organisms, as some forms cut across the two kingdoms e.g Euglena, while 7 others like the bacteria were arbitrarily assigned to the plant kingdom. Several alternative systems were proposed to solve this problem. Six (6) kingdoms previously classified are: Bacteria, Archaea, Protista, Fungi, Plantae, and Animalia  Recently, however, a cladistic classification of all life forms has been proposed based on phylogenic information obtained from molecular data.  According to Woese, Kandler and Wheelis (1990) three monophyletic domains above the kingdoms were recognized.  These are Eukarya (all eukaryotes), Archaea (prokaryotes different from bacteria) and bacteria (the true bacteria).  Based on our current knowledge of phylogenetic tree, protozoans do not belong to the animal kingdom. But since many unicellular forms share animal-like characteristics, they remain of interest to zoologists. Kingdom Animalia, i.e. the metazoans Phylum Porifera Phylum Cnidaria Phylum Ctenophora Phylum Platyhelminthes Phylum Nematoda Phylum Annelida Phylum Mollusca Phylum Arthropoda Phylum Echinodermata Phylum Chordata (Urochordate, Cephalochordate & Vertebrate)  Evolutionary relationships  If you look at photographs of people who share a common ancestor, such as a grandparent or great grandparent, you often see startling similarities in appearance.The people in the photos are obviously related to each other and have inherited some features from their grandparents.  In a natural classification system, biologists group together organisms which are structurally similar and share common ancestors. Current State of Animal Taxonomy 8  The formal taxonomy of animals that we use today was established using the principles of evolutionary systematics and has been revised recently in part using the principles of cladistics.  Introduction of cladistic principles initially replaces paraphyletic groups with monophyletic subgroups while leaving the remaining taxonomy mostly unchanged.  Cladistics is a method of classifying organisms into groups based on their evolutionary history  Monophyletic group: contains an ancestor and all of its descendants.  Paraphyletic group: contains an ancestor but only some of its descendants.  Polyphyletic group: contains various organisms with no recent common ancestor.  A thorough revision of taxonomy along cladistic principles, however, would require profound changes, one of which is abandonment of Linnaean ranks.  A new taxonomic system called PhyloCode is being developed as an alternative to Linnaean taxonomy; this system replaces Linnaean ranks with codes that denote the  nested hierarchy of monophyletic groups conveyed by a cladogram. REPRODUCTION IN ANIMALS  The period of time for which a living organism lives is called lifespan.  Reproduction is the process by which living things produce more of their own kind.  Some animals produce offspring through asexual reproduction while other animals produce offspring through sexual reproduction. Both methods have advantages and disadvantages.  Asexual reproduction produces offspring that are genetically identical to the parent because the offspring are all clones of the original parent.  A single individual can produce offspring asexually and large numbers of offspring can be produced quickly; these are two advantages that asexually reproducing organisms have over sexually reproducing organisms. In a stable or predictable environment, asexual reproduction is an effective means of reproduction because all the offspring will be adapted to that environment.  In an unstable or unpredictable environment, species that reproduce asexually may be at a disadvantage because all the offspring are genetically identical and may not be adapted to different conditions.  During sexual reproduction, the genetic material of two individuals is combined to produce genetically diverse offspring that differ from their parents. The genetic diversity of sexually produced offspring is thought to give sexually reproducing individuals greater fitness because more of their offspring may survive and reproduce in an unpredictable or changing environment. Species that reproduce sexually (and have separate sexes) must maintain two different types of individuals, males and females.  Only half the population (females) can produce the offspring, so fewer offspring will be produced when compared to asexual reproduction. This is a disadvantage of sexual reproduction compared to asexual reproduction.  Asexual Reproduction  Asexual reproduction occurs in prokaryotic microorganisms (bacteria and archaea) and in many eukaryotic, single-celled and multi-celled organisms. There are several ways that animals reproduce asexually, the details of which vary among individual species. 9  Fission  Fission, also called binary fission, occurs in some invertebrate, multi-celled organisms. It is in some ways analogous to the process of binary fission of single-celled prokaryotic organisms.  The term fission is applied to instances in which an organism appears to split itself into two parts and, if necessary, regenerate the missing parts of each new organism.  For example, species of flatworms commonly called the planarians, such as Dugesia dorotocephala, are able to separate their bodies into head and tail regions and then regenerate the missing half in each of the two new organisms.  All monoecious (male & female organs in one animal)  All dioecious (separate and distinct male & female)  Sea anemones (Cnidaria), such as species of the genus Anthopleura will divide along the oral-aboral axis, and  Sea cucumbers (Echinodermata) of the genus Holothuria, will divide into two halves across the oral-aboral axis and regenerate the other half in each of the resulting individuals.  Budding  Budding is a form of asexual reproduction that results from the outgrowth of a part of the body leading to a separation of the “bud” from the original organism and the formation of two individuals, one smaller than the other.  Budding occurs commonly in some invertebrate animals such as hydras and corals.  In Hydra, a bud forms that develops into an adult and breaks away from the main body.  Fragmentation  Fragmentation is the breaking of an individual into parts followed by regeneration. If the animal is capable of fragmentation, and the parts are big enough, a separate individual will regrow from each part.  Fragmentation may occur through accidental damage, damage from predators, or as a natural form of reproduction. Reproduction through fragmentation is observed in sponges, some cnidarians, turbellarians, echinoderms, and annelids. In some sea stars, a new individual can be regenerated from a broken arm and a piece of the central disc.  Parthenogenesis  Parthenogenesis is a form of asexual reproduction in which an egg develops into an individual without being fertilized. The resulting offspring can be either haploid or diploid, depending on the process in the species.  Parthenogenesis occurs in invertebrates such as water fleas, rotifers, aphids, stick insects, and ants, wasps, and bees. Ants, bees, and wasps use parthenogenesis to produce haploid males (drones).  Parthenogenesis has been observed in species in which the sexes were separated in terrestrial or marine zoos.  Sexual reproduction increases genetic diversity  Sexual reproduction allows greater genetic diversity through the processes of meiosis and crossing over.  The first eukaryotes were probably haploid; diploids seem to have arisen on a number of separate occasions by the fusion of haploid cells, which then eventually divided by mitosis. 10  Animals reproduce in two ways:  Some animals reproduce by giving birth to their young ones.  Some animals produce their young ones through eggs.  Viviparous Animal: The animals which give birth to their young ones are called Viviparous animals.  The young babies of these animals feed on their mother’s milk till they learn to eat other food. Such animals are called mammals.  Examples are human, deer, lion and cow.  Majority of mammals are viviparous; the young develop within the uterus and obtain nourishment prior to birth by receiving nutrients from the mother’s blood through a yolk sac placenta, by absorbing a nutritious fluid produced by the uterus, or by eating other eggs.  Ovoviviparous Animal: These animals retain the fertilized eggs in the oviduct, nourished by the egg yolk, the embryos develop into young that are born after hatching within the uterus. Ovoviviparity is a "bridging" form of reproduction between oviparous and viviparous reproduction. Other species of reptiles are ovoviviparous, forming eggs that develop into embryos within the body of the mother Examples are sharks, rays, snakes, fishes, and insects.  Oviparous Animal: The animals lay eggs and then the eggs are fertilized internally, they are then deposited outside the mother’s body to complete their developmental life cycle.  All birds and about 80% of reptile species are oviparous.  Mostly amphibians, fishes, reptiles, birds follow such reproductive strategies.  Insects, molluscs, arachnids, and monotremes are examples of oviparous animals  According to habitat, we can divide oviparous animals into three categories:  Aerial Oviparous animals - Birds  Terrestrial Oviparous animals - Insects and snakes  Aquatic Oviparous animals- Fishes and Tadpoles.  Aerial Oviparous animals  The birds such as hen, crow and parrot lay eggs. They bear their young ones in hard shelled eggs which hatch after some time. Adult birds sit on the eggs for a few days to keep them warm till they hatch. This is called as Incubation.  Terrestrial Oviparous animals: Insects reproduce by laying eggs. Insect eggs are deposited by adult insects in a safe location.  FURTHER READING  Biology by Raven et al 11th  https://opentextbc.ca/biology/chapter/13-1-how-animals-reproduce/ 11  EDWARD CARES BIO LIVING THINGS, CHARACTERISTICS AND REPRODUCTION Living things exist and are alive and are made of microscopic structures called cells. They grow and exhibit movement or locomotion. They experience metabolism, which includes anabolic and catabolic reactions. Living things are capable of producing a new life which is of their own kind through the process of reproduction. CHARACTERISTICS OF LIVING THINGS MOVEMENT: All living things move. It is very obvious that a leopard moves but what about the thorn tree it sits in? Plants too move in various different ways. The movement may be so slow that it is very difficult to see RESPIRATION: Respiration is the release of energy from food substances in all living cells. Living things break down food within their cells to release energy for carrying out the various processes of life. NUTRITION: living things take in food to stay alive. This is digested, absorbed and then assimilated into the body, used for growth, repair and replacement of worn-out tissues and a source of energy for its various activities. IRRITABILITY: the ability to detect and respond to changes in the internal or external environment. All living things are able to sense and respond to stimuli around them such as light, temperature, water, gravity and chemical substances. Organisms can respond to diverse stimuli. For example, plants can grow toward a source of light, climb on fences and walls, or respond to touch. Even tiny bacteria can move toward or away from chemicals (a process called chemotaxis) or light (phototaxis). Movement toward a stimulus is considered a positive response, while movement away from a stimulus is considered a negative response.  GROWTH: Growth is seen in all living things. It involves using food to produce new cells. The permanent increase in cell number and size is called growth. Growth occurs in plants by cell division in special tissues, meristem. EXCERETION: All living things excrete. Excretion is defined as the removal of toxic materials, the waste products of metabolism and substances in excess from the body of an organism. As a result of the many chemical reactions occurring in cells, they have to get rid of waste products which might poison the cells. This does not involve the removal of undigested food i.e. egestion. REPRODUCTION: All living organisms have the ability to produce offspring. Organisms reproduce sexually by making special cells (gametes) which fuse to produce new offsprings or asexually when cell divides into two to form offsprings. COMPETITION: the utilization of the same resources by one or more organisms of the same or different species living together in a community. When the resources such as food, light, space, water, shelter etc are in short supply to meet the needs of all the organisms. Organisms in the population that are unable to compete successfully for these resources die (survival of the fittest). ADAPTATION; Plants have adaptation that help them to survive, live and grow in certain environments. These adaptations help them to make the most of the surrounding area. Differences between living and non-living things: Living Things Non-Living Things They possess life. They do not possess life. Living things are capable of giving birth to their Non-living things do not reproduce. young ones i.e. reproduce  For survival, living things depend on water, air and Non-living things have no such requirements food. Non-living things are not sensitive and do not Living things are sensitive and responsive to stimuli. respond to stimuli. Metabolic reactions constantly occur in all living There are no metabolic reactions in Non-living things. things. Living organisms undergo growth and development. Non-living things do not grow or develop. They have a lifespan and are not immortal. They have no lifespan and are immortal. Living things move from one place to another. Non-living things cannot move by themselves. They respire and the exchange of gases takes place in Non-living things do not respire. their cells. Example: Humans, animals, plants, insects. Example: Rock, pen, buildings, gadgets. REPRODUCTION IN PLANTS Reproduction is one of the most important characteristics of all living beings. It is the production of ones own kind. It is necessary for the continuation of the species on earth and also to replace the dead members of the species. The process by which living organisms produce their offsprings for the continuity of the species is called reproduction. The modes of reproduction vary according to individual species and available conditions. It may be simply by division of the parent cell as in unicellular organisms, by fragmentation of the parent body, by formation of buds and spores, or it may be very elaborate involving development of male and female reproductive organs (stamens and pistils). Irrespective of the mode of reproduction, all organisms pass on their hereditary material to their offsprings during the process of reproduction. MODES OF REPRODUCTION Most plants have roots, stems and leaves. These are called the vegetative parts of a plant. After a certain period of growth, most plants bear flowers. You may have seen the mango trees flowering; it is these flowers that give rise to juicy mango fruit we enjoy. We eat the fruits and usually discard the seeds. Seeds germinate and form new plants. So, what is the function of flowers in plants? Flowers perform the function of reproduction in plants. Flowers are the reproductive parts. In plants, reproduction is carried out via two modes: Asexual Mode Sexual Mode In asexual reproduction plants can give rise to new plants without seeds, whereas in sexual reproduction, new plants are obtained from seeds Asexual Reproduction In Plants In asexual reproduction in plants, plants are reproduced without the formation of seeds. Following are a few ways in which plants reproduce asexually. Vegetative Propagation As the name suggests, reproduction occurs through the vegetative parts of a plant such as stems, leaves, buds, and roots. Plants produced by vegetative propagation take less time to grow and are exact replicas of their parents as they are reproduced from a single parent. Budding It occurs in unicellular plants. A bud-like outgrowth is formed on one side of the parent cell and soon it separates and grows into a new individual e.g. in yeast. Small bulb-like projections arise from yeast cells, eventually detaching itself from the parent cell. This then matures to grow into a new yeast cell. These, in turn, produce more buds and the chain continues forming a number of new yeast cells within a short period of time. Example can also be seen in a multicellular organism; hydra. Fraegmentation You might have seen slimy green patches in ponds, or in other stagnant water bodies. These are the algae. When water and nutrients are available algae grow and multiply rapidly by fragmentation. An alga breaks up into two or more fragments. These fragments or pieces grow into new individual. They multiply rapidly in a short period of time. Other examples can be Planaria (a type of flatworm) and starfish. Spore Formation Spores are present in the air and are covered by a hard protective coat to bear low humidity and high-temperature conditions. Spores germinate and develop into new organisms under favourable conditions. In lower plants including bryophytes and pteridophytes, special reproductive units develop asexually on the parent body. These are called spores. They are microscopic and covered by a protective wall. When they reach the suitable environment they develop into a new plant body e.g. in bread moulds, moss, fern. Advantages of Asexual Reproduction in Plants A large number of plants can be produced within a short period. The exact copies of the parent plant are produced. Many seedless varieties are obtained through the vegetative method. Less attention is required by the plants grown through asexual means than through seeds. Sexual Reproduction In Plants In sexual reproduction, the gametes from male and female reproductive parts of the flower fuse to produce a zygote which develops into an embryo. This embryo remains inside the seed. Seed upon sowing germinates to produce a new plant. The reproductive parts of plants are flowers, Stamen being male reproductive part and pistil being the female reproductive part. If one of these reproductive parts are present in a flower, it is said to be a unisexual flower. Example: papaya. If both Stamen and Pistil are present in flowers they are called bisexual flowers. Example: rose. Pollen grains form the male gametes. The pistil consists of style, stigma, and the Ovary. The ovary consists of one or more ovules. Ovules are where female gametes or the egg is formed. Female and male gametes fuse to form a zygote. The flower is the structure that makes sexual reproduction in flowering plants possible. A wide variety exists in flower appearance, but the function of the flower parts is the same. Their functions are listed below. The stamen – contains the male part of the flower. It produces pollen, a yellow powdery substance. Pollen is produced in the top of the stamen, in a structure called the anther. The pistil – contains the female part of the flower. The top of the pistil is called the stigma. When a pollen grain reaches the pistil, it sticks to the surface of the stigma. The stigma produces a sugar that is used by the pollen to grow a tube. The pollen tube “digs” its way down through the style, allowing delivery of the sperm down to the ovary. This is the enlarged part of the pistil where the female sex cells (eggs) are produced. The eggs are fertilized by the sperm from the pollen tube. The transfer of the pollen from anther to the stigma is called pollination. If allowed to develop without being picked, the ovary dries and splits open to disperse the seeds(s). The petals – of the flower attract insects that carry the pollen from one plant to another. Some plants have no petals and the pollen is carried by the wind. Pollination When pollen is transferred from the anther to the stigma of a flower through carriers such as insects, wind etc it is called pollination. Pollination takes two forms: self pollination and cross pollination. Self-pollination occurs when the pollen from the anther is deposited on the stigma of the same flower, or another  flower on the same plant. Cross pollination is the transfer of pollen from the anther of one flower to the stigma of another flower on a different individual of the same species. FERTILIZATION A zygote is formed as a result of the fusion of gametes which later develops into the embryo. Fruits and seeds are formed post-fertilization. FRUITS AND SEED FORMATION After fertilization, the ovary grows into a fruit and other parts of the flower fall off. The fruit is the ripened ovary. The seeds develop from the ovules. The seed contains an embryo enclosed in a protective seed coat. Some fruits are fleshy and juicy such as mango and orange. Some fruits are hard like almonds and walnut Cell Biology Chapter 1: Understand the cell of as the basic unit of life Chapter 1: Understand the cell of as the basic unit of life 1.1: Cell as a unit of Life. An organism is a life-form—a living entity made up of one or more cells. Although there is no simple definition of life that is endorsed by all biologists, most agree that organisms share a suite of five fundamental characteristics. Cells Organisms are made up of membrane-bound units called cells. The membrane of a cell regulates the passage of materials between exterior and interior spaces. Replication One of the great biologists of the twentieth century, François Jacob, said that the “dream of a bacterium is to become two bacteria.” Almost everything an organism does contributes to one goal: replicating itself. Evolution Organisms are the products of evolution, and their populations continue to evolve today. Information Organisms process hereditary, or genetic, information encoded in units called genes. Organisms also respond to information from the environment and adjust to maintain stable internal conditions. Right now, cells through- out your body are using information to make the molecules that keep you alive; your eyes and brain are decoding information on this page that will help you learn some biology, and if your room is too hot you might be sweating to cool off. Energy To stay alive and reproduce, organisms have to acquire and use energy. To give just two examples: plants absorb sunlight; animals ingest food. 1.2: Biological Levels of Organization: The biological levels of organization of living things follow a hierarchy, such as the one shown in Figure 1.1 From a single organelle to the entire biosphere, living organisms are part of a highly structured hierarchy. Cell Biology Chapter 1: Understand the cell of as the basic unit of life Figure 1.1: Biological Levels of Organization (Campbell and Urry, 2017) Key Points The atom is the smallest and most fundamental unit of matter. The bonding of at least two atoms or more form molecules. The simplest level of organization for living things is a single organelle, which is composed of aggregates of macromolecules. The highest level of organization for living things is the biosphere; it encompasses all other levels. Cell Biology Chapter 1: Understand the cell of as the basic unit of life The biological levels of organization of living things arranged from the simplest to most complex are: organelle, cells, tissues, organs, organ systems, organisms, populations, communities, ecosystem, and biosphere. Key Terms molecule: The smallest particle of a specific compound that retains the chemical properties of that compound; two or more atoms held together by chemical bonds. macromolecule: a very large molecule, especially used in reference to large biological polymers (e.g. nucleic acids and proteins) polymerization: The chemical process, normally with the aid of a catalyst, to form a polymer by bonding together multiple identical units (monomers). Three of the greatest unifying ideas in all of science, which depend on the five characteristics just listed, laid the ground- work for modern biology: the cell theory, the theory of evolution, and the chromosome theory of inheritance. Formally, scientists define a theory as an explanation for a very general class of phenomena or observations that are supported by a wide body of evidence. Note that this definition contrasts sharply with the everyday usage of the word “theory,” which often carries meanings such as “speculation” or “guess.” The cell theory, the theory of evolution, and the chromosome theory of inheritance address fundamental questions: What are organisms made of? Where do they come from? How is hereditary information transmitted from one generation to the next? When these theories emerged in the mid-1800s, they revolutionized the way biologists think about the world. None of these insights came easily, however. The cell theory, for example, emerged after some 200 years of work. 1.3: Cell Theory The microscopes we use today are far more complex than those used in the 1600s by Antony van Leeuwenhoek, a Dutch shopkeeper who had great skill in crafting lenses. Despite the limitations of his now-ancient lenses, van Leeuwenhoek observed the movements of protista (a type of single-celled organism) and sperm, which he collectively termed “animalcules. ” Cell Biology Chapter 1: Understand the cell of as the basic unit of life In a 1665 publication called Micrographia, experimental scientist Robert Hooke coined the term “cell” for the box-like structures he observed when viewing cork tissue through a lens. In the 1670s, van Leeuwenhoek discovered bacteria and protozoa. Later advances in lenses, microscope construction, and staining techniques enabled other scientists to see some components inside cells. By the late 1830s, botanist Matthias Schleiden and zoologist Theodor Schwann were studying tissues and proposed the unified cell theory. The unified cell theory states that: all living things are composed of one or more cells; the cell is the basic unit of life; and new cells arise from existing cells. Rudolf Virchow later made important contributions to this theory. Schleiden and Schwann proposed spontaneous generation as the method for cell origination, but spontaneous generation (also called abiogenesis) was later disproven. Rudolf Virchow famously stated “Omnis cellula e cellula”… “All cells only arise from pre-existing cells. “The parts of the theory that did not have to do with the origin of cells, however, held up to scientific scrutiny and are widely agreed upon by the scientific community today. The generally accepted portions of the modern Cell Theory are as follows: 1. The cell is the fundamental unit of structure and function in living things. 2. All organisms are made up of one or more cells. 3. Cells arise from other cells through cellular division. The expanded version of the cell theory can also include: Cells carry genetic material passed to daughter cells during cellular division All cells are essentially the same in chemical composition Energy flow (metabolism and biochemistry) occurs within cells The generally accepted parts of modern cell theory include: 1. All known living things are made up of one or more cells 2. All living cells arise from pre-existing cells by division. 3. The cell is the fundamental unit of structure and function in all living organisms. 4. The activity of an organism depends on the total activity of independent cells. Cell Biology Chapter 1: Understand the cell of as the basic unit of life 5. Energy flow (metabolism and biochemistry) occurs within cells. 6. Cells contain DNA which is found specifically in the chromosome and RNA found in the cell nucleus and cytoplasm. 7. All cells are basically the same in chemical composition in organisms of similar species. The modern version of the cell theory includes the ideas that: Energy flow occurs within cells. Heredity information (DNA) is passed on from cell to cell. All cells have the same basic chemical composition. 1.4: Size range of cells. Most cells are between 1 and 100 μm in diameter (yellow region of chart) and their components are even smaller (Figure 1.2), as are viruses. Notice that the scale along the left side is logarithmic, to accommodate the range of sizes shown. Starting at the top of the scale with 10m and going down, each reference measurement marks a tenfold decrease in diameter or length. 1.5: Different types of cell Cells—the basic structural and functional units of every organism—are of two distinct types: prokaryotic and eukaryotic. Organisms of the domains Bacteria and Archaea consist of prokaryotic cells. Protists, fungi, animals, and plants all consist of eukaryotic cells. (“Protist” is an informal term refer- ring to a diverse group of mostly unicellular eukaryotes.) All cells share certain basic features: They are all bounded by a selective barrier, called the plasma membrane (also referred to as the cell membrane). Inside all cells is a semifluid, jellylike sub- stance called cytosol, in which subcellular components are suspended. All cells contain chromosomes, which carry genes in the form of DNA. And all cells have ribosomes, tiny complexes that make proteins according to instructions from the genes. Cell Biology Chapter 1: Understand the cell of as the basic unit of life 1 centimeter (cm) = 10–2 meter (m) = 0.4 inch 1 millimeter (mm) = 10–3 m 1 micrometer (μm) = 10–3 mm = 10–6 m 1 nanometer (nm) = 10–3 μm = 10–9 m Figure 1.2: Size ranges of cells (Campbell and Urry, 2017) Cell Biology Chapter 1: Understand the cell of as the basic unit of life As shown in Table 1.1 below, there are some differences between different types of cells (Prokaryotic and Eukaryotic) Table 1.1: Difference between Prokaryotic and Eukaryotic Cells Prokaryotes Eukaryotes Typical bacteria, archaea protists, fungi, plants, animals organisms Name and prokaryotic means “before nucleus” (from Eukaryotic means “true nucleus” evolution the Greek pro, before), reflecting the (from the Greek eu, true, and earlier evolution of prokaryotic cells. karyon, kernel, referring to the nucleus) Typical size ~ 1–5 μm ~ 10–100 μm in diameter Type of nucleoid region; no true nucleus true nucleus with double nucleus membrane DNA circular (usually) linear molecules (chromosomes) with histone proteins DNA location the DNA is concentrated in a region that is most of the DNA is in an organelle not membrane-enclosed, called the called the nucleus, which is nucleoid. bounded by a double membrane. RNA/protein coupled in the cytoplasm RNA synthesis in the nucleus synthesis protein synthesis in the cytoplasm Ribosomes 50S and 30S 60S and 40S Cytoplasmic very few structures highly structured by structure endomembranes and a cytoskeleton Organelle Membrane-bounded structures are absent Membrane-bounded structures are present Cell movement flagella made of flagellin flagella and cilia containing microtubules; lamellipodia and filopodia containing actin Mitochondria none one to several thousand Chloroplasts none in algae and plants Organization usually single cells single cells, colonies, higher multicellular organisms with specialized cells Cell division binary fission (simple division) mitosis (fission or budding) meiosis Chromosomes single chromosome more than one chromosome Membranes cell membrane Cell membrane and membrane- bound organelles Cell Biology Chapter 1: Understand the cell of as the basic unit of life 1.6: Cell size and function Surface Area to Volume Ration The important point is that the surface area to the volume ratio gets smaller as the cell gets larger. Thus, if the cell grows beyond a certain limit, not enough material will be able to cross the membrane fast enough to accommodate the increased cellular volume. When this happens, the cell must divide into smaller cells with favorable surface area/volume ratios, or cease to function. That is why cells are so small. Eukaryotic cells are generally much larger than prokaryotic cells. Size is a general feature of cell structure that relates to function. The logistics of carrying out cellular metabolism sets limits on cell size. At the lower limit, the smallest cells known are bacteria called mycoplasmas, which have diameters between 0.1 and 1.0 μm. These are perhaps the smallest packages with enough DNA to program metabolism and enough enzymes and other cellular equipment to carry out the activities necessary for a cell to sustain itself and reproduce. Typical bacteria are 1–5 μm in diameter, about ten times the size of mycoplasmas. Eukaryotic cells are typically 10–100 μm in diameter. Metabolic requirements also impose theoretical upper limits on the size that is practical for a single cell. At the boundary of every cell, the plasma membrane functions as a selective barrier that allows passage of enough oxygen, nutrients, and wastes to service the entire cell. For each square micrometer of membrane, only a limited amount of a particular substance can cross per second, so the ratio of surface area to volume is critical. As a cell (or any other object) increases in size, its surface area grows proportionately less than its volume. (Area is proportional to a linear dimension squared, whereas volume is proportional to the linear dimension cubed.) Thus, a smaller object has a greater ratio of surface area to volume (Table 1). The scientific skills exercise gives you a chance to calculate the volumes and surface areas of two actual cells— a mature yeast cell and a cell budding from it. The need for a surface area large enough to accommodate the volume helps explain the microscopic size of most cells and the narrow, elongated shapes of others, such as nerve cells. Larger organisms do not generally have larger cells than smaller organisms—they simply have more cells (see Table 1.2). A sufficiently high ratio of surface area to volume is especially important in cells that exchange a lot of material with their surroundings, such as intestinal  Cell Biology Chapter 1: Understand the cell of as the basic unit of life cells. Such cells may have many long, thin projections from their surface called microvilli, which increase surface area without an appreciable increase in volume. Table 1.2 elucidate geometric relationships between surface area and volume. Cells are represented as boxes. Using arbitrary units of length, we can calculate the cell’s surface area (in square units, or units2), volume (in cubic units, or units3), and ratio of surface area to volume. A high surface-to-volume ratio facilitates the exchange of materials between a cell and its environment. Table 1.2: Geometric relationships between surface area and volume Surface area increase while total volume remains constant Total surface area [sum of the surface areas (height × width) of all 6 150 750 box sides × number of boxes] Total volume 1 125 125 [height × width × length × number of boxes] Surface-to-volume (S-to-V) ratio 6 1.2 6 [surface area ÷ volume] 1.7: Eukaryotic Cell Structures and Their Functions The Eukarya domain includes species that range from microscopic algae to 100-meter-tall redwood trees. Protists, fungi, plants, and animals are all eukaryotic. Although multicellularity has evolved several times among eukaryotes, many species are unicellular. The first thing that strikes biologists about eukaryotic cells is how much larger they are on average than bacteria and archaea. Most prokaryotic cells measure 1 to 10 μm in diameter, Cell Biology Chapter 1: Understand the cell of as the basic unit of life while most eukaryotic cells range from about 5 to 100 μm in diameter. For many species of unicellular eukaryotes, this size difference allows them to make a living by ingesting bacteria and archaea whole. Large size has a downside, however. As a cell increases in diameter, its volume increases more than its surface area. In other words, the relationship between them—the surface-areato-volume ratio—changes. Since the surface is where the cell exchanges substances with its environment, the reduction in this ratio decreases the rate of exchange: Diffusion only allows for rapid movement across very small distances. Prokaryotic cells tend to be small enough so that ions and small molecules arrive where they are needed via diffusion. The random movement of diffusion alone, however, is insufficient for this type of transport as the cell’s diameter increases. 1.8: The Benefits of Organelles How are the problems associated with a low surface-area-to volume ratio overcome in eukaryotic cells? The answer lies in their numerous organelles. In effect, the huge volume inside a eukaryotic cell is compartmentalized into many small bins. Because eukaryotic cells are subdivided, the cytosol—the fluid portion between the plasma membrane and these organelles—is only a fraction of the total cell volume. This relatively small volume of cytosol offsets the effects of a low cell surface-area-to-volume ratio with respect to the exchange of nutrients and waste products. 1.9: Compartmentalization also offers two key advantages: 1. Incompatible chemical reactions can be separated. For example, new fatty acids can be synthesized in one organelle while excess or damaged fatty acids are degraded and recycled in a different organelle. 2. Chemical reactions become more efficient. First, the substrates required for particular reactions can be localized and maintained at high concentrations within organelles. When substrates are used up in a particular part of the organelle, they can be replaced by substrates that have only a short distance to diffuse. Second, groups of enzymes that work together can be clustered within or on the membranes of organelles instead of floating free in the cytosol. When the product of one reaction is the substrate for a second reaction, clustering the two enzymes increases the speed and efficiency of both reactions. If bacterial and archaeal cells can be compared to specialized machine shops, then eukaryotic cells resemble sprawling industrial complexes. The organelles and other structures found in Cell Biology Chapter 1: Understand the cell of as the basic unit of life eukaryotes are like highly specialized buildings that act as administrative centers, factories, transportation corridors, waste and recycling facilities, warehouses, and power stations. When typical prokaryotic and eukaryotic cells are compared, three key differences stand out: 1. Eukaryotic cells are generally much larger than prokaryotic cells. 2. Prokaryotic chromosomes are in a loosely defined nucleoid region while eukaryotic chromosomes are enclosed within a membrane-bound compartment called the nucleus. 3. The cytoplasm of eukaryotic cells is compartmentalized into a larger number of distinct organelles compared to the cytoplasm in prokaryotic cells. Eukaryotic Cell Structures: Figure 1.3 provides a simplified view of a typical animal cell and a plant cell. The artist has removed most of the cytoskeletal elements to make the organelles and other cellular parts easier to see. As you read about each cell component in the pages that follow, focus on identifying how its structure correlates with its function. Figure 1.3a Overview of Eukaryotic Cells. Generalized images of an animal cell that illustrate the cellular structures in the “typical” eukaryote. The structures have been color-coded for clarity (Freeman et al., 2017). Cell Biology Chapter 1: Understand the cell of as the basic unit of life Figure 1.3b Overview of Eukaryotic Cells. Generalized images of a plant cell that illustrate the cellular structures in the “typical” eukaryote. the structures have been color-coded for clarity. Compare with the prokaryotic cell, shown at true relative size at bottom left (Freeman et al., 2017). 1.10: Cell inclusions and organelles. What are Cell Organelles? The cellular components are called cell organelles. These cell organelles include both membrane and non-membrane bound organelles, present within the cells and are distinct in their structures and functions. They coordinate and function efficiently for the normal functioning of the cell. A few of them function by providing shape and support, whereas some are involved in the locomotion and reproduction of a cell. There are various organelles present within the cell and are classified into three categories based on the presence or absence of membrane. Organelles without membrane: The Cell wall, Ribosomes, and Cytoskeleton are non- membrane-bound cell organelles. They are present both in prokaryotic cell and the eukaryotic cell. Single membrane-bound organelles: Vacuole, Lysosome, Golgi Apparatus, Endoplasmic Reticulum are single membrane-bound organelles present only in a eukaryotic cell. Cell Biology Chapter 1: Understand the cell of as the basic unit of life Double membrane-bound organelles: Nucleus, mitochondria and chloroplast are double membrane-bound organelles present only in a eukaryotic cell. 1.11: Functions of cell organelles Plasma Membrane The plasma membrane of a cell is a network of lipids and proteins that forms the boundary between a cell’s contents and the outside of the cell. It is also simply called the cell membrane. The main function of the plasma membrane is to protect the cell from its surrounding environment. It is semi-permeable and regulates the materials that enter and exit the cell. The cells of all living things have plasma membranes. Functions of the Plasma Membrane A Physical Barrier The plasma membrane surrounds all cells and physically separates the cytoplasm, which is the material that makes up the cell, from the extracellular fluid outside the cell. This protects all the components of the cell from the outside environment and allows separate activities to occur inside and outside the cell. The plasma membrane provides structural support to the cell. It tethers the cytoskeleton, which is a network of protein filaments inside the cell that hold all the parts of the cell in place. This gives the cell its shape. Certain organisms such as plants and fungi have a cell wall in addition to the membrane. The cell wall is composed of molecules such as cellulose. It provides additional support to the cell, and it is why plant cells do not burst like animal cells do if too much water diffuses into them. Selective Permeability Plasma membranes are selectively permeable (or semi-permeable), meaning that only certain molecules can pass through them. Water, oxygen, and carbon dioxide can easily travel through the membrane. Generally, ions (e.g. sodium, potassium) and polar molecules cannot pass through the membrane; they must go through specific channels or pores in the membrane Cell Biology Chapter 1: Understand the cell of as the basic unit of life instead of freely diffusing through. This way, the membrane can control the rate at which certain molecules can enter and exit the cell. Endocytosis and Exocytosis Endocytosis is when a cell ingests relatively larger contents than the single ions or molecules that pass through channels. Through endocytosis, a cell can take in large quantities of molecules or even whole bacteria from the extracellular fluid. Exocytosis is when the cell releases these materials. The cell membrane plays an important role in both of these processes. The shape of the membrane itself changes to allow molecules to enter or exit the cell. It also forms vacuoles, small bubbles of membrane that can transport many molecules at once, in order to transport materials to different places in the cell. Cell Signalling Another important function of the membrane is to facilitate communication and signalling between cells. It does so through the use of various proteins and carbohydrates in the membrane. Proteins on the cell “mark” that cell so that other cells can identify it. The membrane also has receptors that allow it to carry out certain tasks when molecules such as hormones bind to those receptors. Plasma Membrane Structure Figure 1.4: Shows the fluid mosaic model of the plasma membrane where integral membrane proteins are inserted into the lipid bilayer, whereas peripheral proteins are bound to the membrane indirectly by protein–protein interactions. Most integral membrane proteins are transmembrane proteins with portions exposed on both sides of the lipid bilayer. The extracellular portions of these proteins are usually glycosylated, as are the peripheral membrane proteins bound to the external face of the membrane. Phospholipids The membrane is partially made up of molecules called phospholipids, which spontaneously arrange themselves into a double layer with hydrophilic (“water loving”) heads on the outside and hydrophobic (“water hating”) tails on the inside. These interactions with water are what allow plasma membranes to form. Cell Biology Chapter 1: Understand the cell of as the basic unit of life Proteins Proteins are wedged between the lipids that make up the membrane, and these transmembrane proteins allow molecules that couldn’t enter the cell otherwise to pass through by forming channels, pores or gates. In this way, the cell controls the flow of these molecules as they enter and exit. Proteins in the cell membrane play a role in many other functions, such as cell signaling, cell recognition, and enzyme activity. Carbohydrates Carbohydrates are also found in the plasma membrane; specifically, most carbohydrates in the membrane are part of glycoproteins, which are formed when a carbohydrate attaches to a protein. Glycoproteins play a role in the interactions between cells, including cell adhesion, the process by which cells attach to each other. Fluid Mosaic Model Technically, the cell membrane is a liquid. At room temperature, it has about the same consistency as vegetable oil. Lipids, proteins, and carbohydrates in the plasma membrane can diffuse freely throughout the cell membrane; they are essentially floating across its surface. This is known as the fluid mosaic model, which was coined by S.J. Singer and G.L. Nicolson in 1972. According to the fluid mosaic model, the plasma membranes are subcellular structures, made of a lipid bilayer in which the protein molecules are embedded (Figure 1.4 ). Figure 1.4: Shows the fluid mosaic model of the plasma membrane Cell Biology Chapter 1: Understand the cell of as the basic unit of life Cytoplasm The cytoplasm is present both in plant and animal cells. They are jelly-like substances, found between the cell membrane and nucleus. They are mainly composed of water, organic and inorganic compounds. The cytoplasm is one of the essential components of the cell, where all the cell organelles are embedded. These cell organelles contain enzymes, mainly responsible for controlling all metabolic activity taking place within the cell and are the site for most of the chemical reactions within a cell. Nucleus The nucleus is a double-membraned organelle found in all eukaryotic cells (Figure 1.5). It is the largest organelle, which functions as the control centre of the cellular activities and is the storehouse of the cell’s DNA. By structure, the nucleus is dark, round, surrounded by a nuclear membrane. It is a porous membrane (like cell membrane) and forms a wall between cytoplasm and nucleus. Within the nucleus, there are tiny spherical bodies called nucleolus. It also carries another essential structure called chromosomes. Chromosomes are thin and thread-like structures which carry another important structure called a gene. Genes are a hereditary unit in organisms i.e., it helps in the inheritance of traits from one generation (parents) to another (offspring). Hence, the nucleus controls the characters and functions of cells in our body. The primary function of the nucleus is to monitor cellular activities including metabolism and growth by making use of DNA’s genetic information. Nucleoli in the nucleus are responsible for the synthesis of protein and RNA. Figure 1.5: Diagram of nucleus Cell Biology Chapter 1: Understand the cell of as the basic unit of life Endoplasmic Reticulum The Endoplasmic Reticulum is a network of membranous canals filled with fluid. They are the transport system of the cell, involved in transporting materials throughout the cell. There are two different types of Endoplasmic Reticulum: 1. Rough Endoplasmic Reticulum – They are composed of cisternae, tubules, and vesicles, which are found throughout the cell and are involved with protein manufacture. 2. Smooth Endoplasmic Reticulum – They are the storage organelle, associated with the production of lipids, steroids, and also responsible for detoxifying the cell. Mitochondria Mitochondria are called the powerhouses of the cell as they produce energy-rich molecules for the cell. The mitochondrial genome is inherited maternally in several organisms. It is a double membrane-bound, sausage-shaped organelle, found in almost all eukaryotic cells. The double membranes divide its lumen into two distinct aqueous compartments. The inner compartment is called ‘matrix’ which is folded into cristae whereas the outer membrane forms a continuous boundary with the cytoplasm. They usually vary in their size and are found either round or oval in shape. Mitochondria are the sites of aerobic respiration in the cell, produces energy in the form of ATP and helps in the transformation of the molecules. For instance, glucose is converted into adenosine triphosphate – ATP. Mitochondria have their own circular DNA, RNA molecules, ribosomes (the 70s), and a few other molecules that help in protein synthesis. Figure 1.6: Diagram of Mitochondria Cell Biology Chapter 1: Understand the cell of as the basic unit of life Plastids Plastids are large, membrane-bound organelles which contain pigments (Figure 1.7). Based on the type of pigments, plastids are of three types: Figure 1.7: Diagram of Plasmid Chloroplasts – Chloroplasts are double membrane-bound organelles, which usually vary in their shape – from a disc shape to spherical, discoid, oval and ribbon. They are present in mesophyll cells of leaves, which store chloroplasts and other carotenoid pigments. These pigments are responsible for trapping light energy for photosynthesis. The inner membrane encloses a space called the stroma. Flattened disc-like chlorophyll-containing structures known as thylakoids are arranged in a stacked manner like a pile of coins. Each pile is called as granum (plural: grana) and the thylakoids of different grana are connected by flat membranous tubules known as stromal lamella. Just like the mitochondrial matrix, the stroma of chloroplast also contains a double-stranded circular DNA, 70S ribosomes, and enzymes which required for the synthesis of carbohydrates and proteins. Chromoplasts – The chromoplasts include fat-soluble, carotenoid pigments like xanthophylls, carotene, etc. which provide the plants with their characteristic color – yellow, orange, red, etc. Leucoplasts – Leucoplasts are colorless plastids which store nutrients. Amyloplasts store carbohydrates (like starch in potatoes), aleuroplasts store proteins, and elaioplasts store oils and fats. Cell Biology Chapter 1: Understand the cell of as the basic unit of life Ribosomes Ribosomes are nonmembrane-bound and important cytoplasmic organelles found in close association with the endoplasmic reticulum. Ribosomes are found in the form of tiny particles in a large number of cells and are mainly composed of 2/3rd of RNA and 1/3rd of protein. They are named as the 70s (found in prokaryotes) or 80s (found in eukaryotes) The letter S refers to the density and the size, known as Svedberg’s Unit. Both 70S and 80S ribosomes are composed of two sub-units. Ribosomes are either encompassed within the endoplasmic reticulum or are freely traced in the cell’s cytoplasm. Ribosomal RNA and Ribosomal proteins are the two components that together constitute ribosomes. The primary function of the ribosomes includes protein synthesis in all living cells that ensure the survival of the cell. Golgi Apparatus Golgi Apparatus also termed as Golgi Complex. It is a membrane-bound organelle, which is mainly composed of a series of flattened, stacked pouches called cisternae. This cell organelle is primarily responsible for transporting, modifying, and packaging proteins and lipid to targeted destinations. Golgi Apparatus is found within the cytoplasm of a cell and are present in both plant and animal cells. Microbodies Microbodies are membrane-bound, minute, vesicular organelles, found in both plant and animal cell. They contain various enzymes and proteins and can be visualized only under the electron microscope. Cytoskeleton It is a continuous network of filamentous proteinaceous structures that run throughout the cytoplasm, from the nucleus to the plasma membrane. It is found in all living cells, notably in the eukaryotes. The cytoskeleton matrix is composed of different types of proteins that can divide rapidly or disassemble depending on the requirement of the cells. The primary functions include providing the shape and mechanical resistance to the cell against deformation, the contractile nature of the filaments helps in motility and during cytokinesis. Cell Biology Chapter 1: Understand the cell of as the basic unit of life Cilia and Flagella Cilia are hair-like projections, small structures, present outside the cell wall and work like oars to either move the cell or the extracellular fluid. Flagella are slightly bigger and are responsible for the cell movements. The eukaryotic flagellum structurally differs from its prokaryotic counterpart. The core of the cilium and flagellum is called a axoneme, which contains nine pairs of gradually arranged peripheral microtubules and a set of central microtubules running parallel to the axis. The central tubules are interconnected by a bridge and are embedded by a central sheath. One of the peripheral microtubular pairs is also interconnected to the central sheath by a radial spoke. Hence there is a total of 9 radial spokes. The cilia and flagella emerge from centriole-like structures called basal bodies. Centrosome and Centrioles The centrosome organelle is made up of two mutually perpendicular structures known as centrioles. Each centriole is composed of 9 equally spaced peripheral fibrils of tubulin protein, and the fibril is a set of interlinked triplets (Figure 1.8). The core part of the centriole is known as a hub and is proteinaceous. The hub connects the peripheral fibrils via radial spoke, which is made up of proteins. The centrioles from the basal bodies of the cilia and flagella give rise to spindle fibres during cell division. Figure 1.8: Diagram of centriole Vacuoles Vacuoles are mostly defined as storage bubbles of irregular shapes which are found in cells. They are fluid-filled organelles enclosed by a membrane. The vacuole stores the food or a Cell Biology Chapter 1: Understand the cell of as the basic unit of life variety of nutrients that a cell might need to survive. In addition to this, it also stores waste products. The waste products are eventually thrown out by vacuoles. Thus, the rest of the cell is protected from contamination. The animal and plant cell have different size and number of vacuoles. Compared to the animals, plant cell have larger vacuoles. Table 1.3 below described each cell organelle and their functions Table 1.3: A Brief Summary on Cell Organelles Cell Structure Functions Organelles Cell membrane A double membrane composed of Provides shape, protects the inner lipids and proteins. Present both in organelle of the cell and acts as a plant and animal cell. selectively permeable membrane. Centrosomes Composed of Centrioles and It plays a major role in organizing the found only in the animal cells. microtubule and Cell division. Chloroplasts Present only in plant cells and Sites of photosynthesis. contains a green-coloured pigment known as chlorophyll. Cytoplasm A jelly-like substance, which Responsible for the cell’s metabolic consists of water, dissolved activities. nutrients and waste products of the cell. Endoplasmic A network of membranous Forms the skeletal framework of the Reticulum tubules, present within the cell, involved in the Detoxification, cytoplasm of a cell. production of Lipids and proteins. Golgi Membrane-bound, sac-like It is mainly involved in secretion and apparatus organelles, present within the intracellular transport. cytoplasm of the eukaryotic cells. Lysosomes A tiny, circular-shaped, single Helps in the digestion and removes membrane-bound wastes and digests dead and damaged organelles, filled with digestive cells. Therefore, it is also called as the enzymes. “suicidal bags”. Mitochondria An oval-shaped, membrane- The main sites of cellular respiration bound organelle, also called as the and also involved in storing energy in “Power House of The Cell”. the form of ATP molecules. Cell Biology Chapter 1: Understand the cell of as the basic unit of life Nucleus A largest, double membrane- Controls the activity of the cell, helps bound organelles, which contains in cell division and controls the all the cell’s genetic information. hereditary characters. Peroxisome A membrane-bound cellular Involved in the metabolism of lipids organelle present in the and catabolism of long-chain fatty cytoplasm, which contains the acids. reducing enzyme. Plastids Double membrane-bound Helps in the process of photosynthesis organelles. There are 3 types of and pollination, Imparts colour for plastids: leaves, flowers and fruits and stores 1. Leucoplast –Colourless starch, proteins and fats. plastids. 2. Chromoplast–Blue, Red, and Yellow colour plastids. 3. Chloroplast – Green coloured plastids. Ribosomes Non-membrane organelles, found Involved in the Synthesis of Proteins. floating freely in the cell’s cytoplasm or embedded within the endoplasmic reticulum. Vacuoles A membrane-bound, fluid-filled Provide shape and rigidity to the plant organelle found within the cell and helps in digestion, excretion, cytoplasm. and storage of substances. 1.12: Difference Between Plant cell and Animal cell In an ecosystem, plants have the role of producers while animals have taken the role of consumers. Hence, their daily activities and functions vary, so do their cell structure. Cell structure and organelles vary in plants and animals, and they are primarily classified based on their function. The difference in their cell composition is the reason behind the difference between plants and animals, their structure and functions Table 1.4. Each cell organelle has a particular function to perform. Some of the cell organelles are present in both plant cell and the animal cell, while others are unique to just one. Most of the earth’s higher organisms are eukaryotes, including all plant and animals. Hence, these cells share some similarities typically associated with eukaryotes. For example, all eukaryotic cells consist of a nucleus, plasma membrane, cytoplasm, peroxisomes, mitochondria, ribosomes and other cell organelles. Cell Biology Chapter 1: Understand the cell of as the basic unit of life Differences Between Plant Cell and Animal Cell As stated above, both plant and animal cells share a few common cell organelles, as both are eukaryotes. The function of all these organelles is said to be very much similar. However, the major differences between the plant and animal cells, which significantly reflect the difference in the functions of each cell. Table 1.4: The major differences between the plant cell and animal cell are mentioned below: Plant Cell Animal Cell Cell Shape Square or rectangular in shape Irregular or round in shape Cell wall Present Absent Plasma/cell Present Present membrane Endoplasmic Present Present Reticulum Nucleus Present and lies on one side of the Present and lies in the centre cell of the cell Lysosomes Present but are very rare Present Centrosomes Absent Present Golgi Apparatus Present Present Cytoplasm Present Present Ribosomes Present Present Plastids Present Absent Vacuoles Few large or a single, centrally Usually small and numerous positioned vacuole Cilia Absent Present in most of the animal cells Mitochondrial Present but fewer in number Present and are numerous Mode of Nutrition Primarily autotrophic Heterotrophic Conclusion Both plant and animal cells comprise membrane-bound organelles, such as endoplasmic reticulum, mitochondria, the nucleus, Golgi apparatus, peroxisomes, lysosomes. They also have similar membranes, such as cytoskeletal elements and cytosol. The plant cell can also be larger than the animal cell. The normal range of the animal cell varies from about 10 – 30 micrometres and that of plant cell range between 10 – 100 micrometres. Cell Biology Chapter 1: Understand the cell of as the basic unit of life 1.13: Effects of hypertonic, hypotonic and isotonic solutions on the cell plasma The effects of hypotonic, hypertonic and isotonic solution on animal and plant cells. Hypertonic - Concentration with higher solute concentration and less water concentration Hypotonic - lower solute concentration and more water concentration Isotonic - Solution in which water molecule and solute molecule are equal in concentration. Animal and plant cell In an isotonic solution Isotonic solution is a solution in which the concentration of solutes is equal, so: - Water diffuses into and out of the cell at equal rates. - There’s no net movement of water across the plasma membrane - The cells retain their normal shape Animal and plant cells in a hypotonic solution Solution which contain higher concentration of water and lower concentration of solutes is called as hypotonic solution. Since the concentration of water is higher outside the cell, there is a net movement of water from outside into the cell. Cell gains water, swells and the internal pressure increases. Eventually burst (haemolysis). The effects of hypertonic solution in animal and plant cell Contain higher concentration of solutes and less of water than a cell. Since the concentration of water is higher within the cell, there is a net movement of water from inside to outside of the cell. (water leaves the cell by osmosis) Causes the cell to shrink as its internal pressure decreases. Hypertonic solution on plant cell Water diffuses out of the large central vacuole by osmosis. Water lose from both vacuole and cytoplasm cause to shrink. Plasma membrane pulls away from the cell wall. (plasmolysis). Become flaccid and less turgid. Cell wall doesn’t shrink because it is strong and rigid. If plasmolysis continues, death may result. If we placed the plasmolysed plant cell in a hypotonic solution (pure water), water moves into the cell by osmosis and become turgid again. (deplasmolysis) Cell Biology Chapter 1: Understand the cell of as the basic unit of life Food preservation The concept of osmosis and diffusion are applied in the preservation of food, such as fruits, fish and vegetables by using preservatives (salt, sugar/vinegar) Salt solution of hypertonic to tissue of fish. So water leaves the fish tissue and enter the salt solution by osmosis. Fish become dehydrated and cell crenate. Therefore, bacteria can’t grow in fish tissue and bacteria cell will crenate. Preserved fish don’t decay so soon and last longer. Preservation with vinegar Mangoes are soaked in vinegar which has low pH, vinegar diffuses into the tissues of the mangoes and become acidic. Low pH prevents the growth of microorganism in mangoes and preserved mangoes can last longer.  BIO 101 Topic: Heredity and evolution: Introduction to Darwinism and Lamarkism, Mendelian laws, explanation of key genetic terms By Dr. A. T. Anifowoshe Department of Zoology University of Ilorin, Ilorin, Nigeria ---------------------------------------------------------------------------------------------------------------- Hereditary and Evolution Heredity Heredity refers to the process through which genetic information is passed from one generation to the next. It is mediated through genes, which are segments of DNA that code for specific traits. Types of Heritable Characters: 1. Physical Traits: These traits are controlled by genes and influenced by alleles inherited from both parents. Examples: Eye color, height, skin color, hair texture etc 2. Physiological Traits: Such traits are encoded by specific genes that regulate biochemical and physiological processes. Examples: Blood type, metabolic rates, and immune responses. 3. Behavioral Traits: Examples: Certain instinctual behaviors and predispositions to learning or temperament. Often influenced by both genetic and environmental factors. 4. Disease Susceptibility: Such traits are often controlled by one or multiple genes. Examples: Inherited disorders like sickle cell anemia, cystic fibrosis, or predisposition to conditions like diabetes or heart disease. Role of Chromosomes in Heredity and Heritable Characters Introduction: Chromosomes are vital structures within cells that carry genetic material in the form of DNA. They play a fundamental role in heredity, serving as the medium through which genetic information is passed from parents to offspring. Chromosomes house genes, the functional units of heredity, which determine an organism's traits, or heritable characters. Role of Chromosomes in Heredity 1. Carriers of Genetic Information: Chromosomes are made up of DNA and proteins. The DNA contains sequences called genes, which encode the instructions for the development and functioning of living organisms. In the nucleus of each cell, DNA molecule is packaged into thread-like structures called Chromosomes. It was first described by Straubberg (1875) and was coined by Waldeyer in 1888. Each chromosome is made up of DNA tightly coiled by proteins called Histones. 2. Transmission During Cell Division: i. Mitosis: Ensures that genetic information is faithfully copied and distributed to daughter cells, maintaining genetic consistency within an organism. ii. Meiosis: Halves the chromosome number in gametes (sperm and egg cells), ensuring that offspring inherit the correct number of chromosomes when gametes fuse during fertilization. 3. Chromosome Structure and Function: i. Chromosome Number: Each species has a specific chromosome number (e.g., humans have 46 chromosomes arranged in 23 pairs). This number is critical for maintaining the integrity of an organism's genetic code. ii. Homologous Chromosomes: Chromosomes come in pairs, one from each parent, and contain alleles of the same genes, which may differ in their expression. Organisms No. of Chromosomes (2n) Human 46 Dog 78 Chimpanzee 48 Horse 64 Chicken 78 Fruit-fly 8 Mosquito 6 Nematode 11(m), 12(f) Rice, Tomatoes 24 Maize, Carrot 20  4. Role in Genetic Variation: i. Crossing Over: During meiosis, homologous chromosomes exchange genetic material, leading to new combinations of alleles in offspring. ii. Independent Assortment: The random distribution of chromosomes to gametes during meiosis contributes to genetic diversity. 5. Sex Determination: Chromosomes, particularly sex chromosomes (X and Y in humans), determine the sex of the offspring. Females typically have two X chromosomes (XX), while males have one X and one Y chromosome (XY). Evolution Evolution is the process through which species undergo changes in their genetic makeup over successive generations, leading to the emergence of new species, adaptation to environments, and biological diversity. Concepts in Evolution 1. Natural Selection: Proposed by Charles Darwin, natural selection suggests that organisms with favorable traits are more likely to survive, reproduce, and pass on those traits to their offspring. 2. Variation: Genetic variation within a population is crucial for evolution. It arises from mutations, genetic recombination during sexual reproduction, and gene flow between populations. 3. Adaptation: Traits that improve an organism's ability to survive and reproduce in its environment become more common over generations. 4. Speciation: The process by which new species arise. This can occur due to geographic isolation, reproductive barriers, or adaptive radiation.  5. Evidence of Evolution: i. Fossil Records: Show gradual changes in species over time. ii. Comparative Anatomy: Homologous structures suggest common ancestry. iii. Genetics: Similarities in DNA sequences across species support evolutionary relationships. 1. Darwinism (Theory of Evolution by Natural Selection) Charles Darwin's theory, presented in On the Origin of Species (1859), suggests that species evolve over time through natural selection. This process is based on the following principles:  Variation: Within any species, individuals exhibit variations in traits, some of which are heritable.  Competition: Due to limited resources, there is a struggle for survival among individuals.  Adaptation: Traits that improve an individual’s chances of survival (e.g., camouflage, speed) become more common in the population over generations.  Survival of the Fittest: Individuals with favorable adaptations are more likely to survive, reproduce, and pass these traits to the next generation. 2. Lamarckism (Theory of Inheritance of Acquired Characteristics) Lamarckism was proposed by Jean-Baptiste de Monet Lamarck in the year 1744-1829. This theory was based on the principle that all the physical changes occurring in an individual during its lifetime are inherited by its offspring. For eg., the development of an organ when used many times.  Use and Disuse: Body parts that are frequently used become stronger and more developed, while unused parts weaken and may disappear.  Inheritance of Acquired Traits: Traits developed over an organism's life due to environmental adaptation are passed to offspring. Example: Lamarck suggested that giraffes have long necks because their ancestors stretched their necks to reach leaves on tall trees. Critique: Lamarckism lacks evidence as acquired traits do not alter genetic information in a way that can be inherited. For instance, a bodybuilder’s muscles do not pass to their children. 3. Mendelian Laws of Inheritance Gregor Mendel, known as the "Father of Genetics," discovered basic principles of inheritance by studying pea plants. His findings led to the formulation of Mendelian laws: Law of Dominance This i