Characteristics of Living Organisms

• In order for something to be considered 'living', it must fulfil specific criteria that are true of all living organisms

• Viruses are a good example of non-living particles/agents

• These criteria can be remembered using the acronym MRS H GREN, which stands for:

Movement

• Movement is an action by an organism causing a change of position or place

• The movement of an organism from place to place is called locomotion

• Plants cannot move from place to place but can change their orientation

  • For example, sunflowers track the sun and so change their orientation throughout the day

Respiration

Respiration:

• Respiration is a chemical reaction carried out in all living organisms

• Energy is released from glucose either in the presence of oxygen (aerobic respiration) or the absence of oxygen (anaerobic respiration)

• The reactions ultimately result in the production of carbon dioxide and water as waste products

• Energy is transferred in the form of ATP

Sensitivity

• The sensitivity of an organism refers to its ability to detect and respond to stimuli in its surroundings

• Responding to the environment around them gives an organism the best chances of survival (survival of the fittest)

Sensitivity responses in:

1. Animals

   • In humans, the nervous system provides a complex system of receptors, neurons and effectors which detect and respond to different stimuli using electrical impulses

   • The endocrine system also allows a response to stimuli using chemical messengers, which travel in the blood, called hormones

2. Plants

   • In plants, responses are controlled by chemicals and are usually much slower

     • Geotropism describes a plants response to gravity which causes the roots to grow down into the soil

     • Phototropism describes a plants response to light which causes shoots to grow towards sunlight

Homeostasis

Homeostasis in:

1. Humans

   • Thermoregulation refers to the control of body temperature

   • The optimum human body temperature is 37°C

     • If body temperature increases e.g. during exercise, mechanisms for control will be initiated to return the temperature back to the optimum

     • Mechanisms include sweating or vasodilation

   • Other homeostatic mechanisms in humans include glucoregulation (control of blood glucose levels) and osmoregulation (control of water levels)

2. Plants

   • Water evaporates from the stomata on the underside of the leaf, leading to heat loss, this is called transpiration

Growth

• Growth is defined as a permanent increase in size

  • In animals, an individual grows larger between the zygote and adult stage with changes in proportion or shape

  • In plants, an individual grows larger throughout their whole life with new shoots, leaves, branches etc. forming year after year

Reproduction

• Reproduction is the process that leads to the production of more of the same kind of organism

• Reproduction is fundamental to the survival of a population and ultimately, the species

• There are different types of reproduction:

  • Sexual reproduction

    • In this type of reproduction, the male and female gametes fuse together

  • Asexual reproduction

    • There is only one parent involved so an exact clone is produced

Excretion

Excretion

• Chemical reactions that take place inside living cells are described as metabolic reactions producing waste products, some of which may be toxic

• Excretion is the removal of toxic materials and substances from organisms’

• Excretion in:

  1. Animals

     • Waste products excreted by animals include:

       • Carbon dioxide from respiration

       • Water from respiration and other chemical reactions

       • Urea which contains nitrogen resulting from the breakdown of proteins

  

  2. Plants

     • Waste products excreted by plants include:

       • Oxygen from photosynthesis

       • Carbon dioxide from respiration

       • Water from respiration and other chemical reactions

Nutrition

Nutrition in:

1. Plants

   • Plants use sunlight, carbon dioxide and water to produce oxygen and glucose in the process of photosynthesis

   • Because plants create their own food for energy, they are described as being autotrophic

2. Animals

   • Animals consume other living organisms in order to obtain the energy they require

   • They break down larger complex molecules into simpler molecules through the process of digestion

   • As animals obtain their food from a range of different sources, they are described as being heterotrophic

Eukaryotic Organisms

• All living organisms can be grouped or 'classified' using a classification system that consists of five kingdoms.

• Eukaryotic organisms can be multicellular or single-celled and are made up of cells that contain a nucleus with a distinct membrane

• Only 4 of them are classified as eukaryotic organisms, and those are:

Animals

• Animals are multicellular

• They often store carbohydrates as glycogen

• They usually have nervous coordination

Plants

• They are multicellular

• They store carbohydrates as starch or sucrose

• They do not have nervous coordination

Fungi

• They can be both unicellular and multicellular

  • Multicellular fungi are mainly made up of thread-like structures known as hyphae that contain many nuclei and are organized into a network known as a mycelium

• Some fungi are parasitic and feed on living material

• Some fungi store carbohydrates as glycogen

• They do not have nervous coordination

Protoctists

• They are mainly microscopic and single-celled but some aggregate (group together) into larger forms, such as colonies or chains of cells that form filaments

• Some have features making them more like animal cells e.g. Plasmodium (the protoctist that causes malaria)

• Some have features, such as cell walls and chloroplasts, making them more like plant cells e.g. green algae, such as Chlorella

Prokaryotic Organisms

• Prokaryotes do not have a nucleus, but instead the nuclear material of prokaryotic cells is found in the cytoplasm

• Bacteria are prokaryotic organisms

• Viruses can only reproduce inside living host cells. The virus derives benefits while the relationship harms the host.

• Examples of bacteria include:

  • Lactobacillus (a rod-shaped bacterium used in the production of yoghurt from milk)

  • Pneumococcus (a spherical bacterium that acts as the pathogen causing pneumonia)

• Bacteria feed in different ways:

  • Some bacteria can carry out photosynthesis despite having no chloroplasts. This is because they still possess chlorophyl and enzymes necessary to synthesise sugars from carbon dioxide.

  • Most feed on other living or dead organisms (if they feed on dead organic matter then they are known as saprobionts or decomposers)

Pathogens

• A pathogen is any microorganism that causes disease in another organism (e.g. in plants or animals)

• Many microorganisms are pathogens including:

  • Bacteria

  • Fungi

  • Protoctists

  • Viruses

• Not all species within these groups (apart from the viruses) are pathogens, as many bacteria, fungi and protoctists are harmless and do not cause disease

• However, all viruses are pathogenic as they can only exist by living inside the living cells of other organisms (or by using these cells to create more viruses)

Pathogenic bacteria

• Pathogenic bacteria do not always infect the hosts of cells, they can remain within body cavities or spaces

• M. tuberculosis causes tuberculosis (TB) in humans

  • The bacteria infect the lungs, causing a chronic cough and bloody mucus

  • It is a disease often associated with poor hygiene and sanitation

  • M. bovine in cows can also transmit to humans to cause TB

Pathogenic fungi

• Fungal diseases are much more common in plants than animals

• Cattle ringworm and athletes foot are fungal diseases that exist on the surface of the skin

• Fungal diseases in plants tend to be much more serious and can threaten entire crops

• Black Sigatoka is a fungal disease in bananas

  • It spreads through the leaves of the plant, reducing its ability to photosynthesise

  • The lack of photosynthesis causes parts of the leaf to die; producing black streaks

  • Eventually, the whole leaf dies

Pathogenic protoctists

• Plasmodium falciparum is a protoctist that causes severe forms of malaria in humans

  • The parasite is spread by mosquitoes

  • Infected individuals experience fever, chills and fatigue

Viruses:

• Viruses since they are not alive, only do reproduction but even to carry out this process they must take over a host cell’s metabolic pathways in order to make multiple copies of themselves

• Viruses, which have a wide variety of shapes and sizes, all share the following biological characteristics:

  • They are small particles (always smaller than bacteria)

  • They are parasitic and can only reproduce inside living cells

  • They infect every type of living organism

  • They have no cellular structure but have a protein coat and contain one type of nucleic acid, either DNA or RNA

Influenza virus

• Three different influenza viruses infect humans to cause the flu

  • Influenza A, influenza B and influenza C infect the cells that line the airways

  • They cause a high temperature, body aches and fatigue

  • Influenza A is the virus that causes the most cases of flu globally