The unifying characteristics of living organisms

·        In order for something to be considered ‘living’, it must fulfill specific criteria that are true of all living organisms.

·        These criteria can be remembered using the acronym MRS C GREN

o   Movement

o   Respiration

o   Sensitivity

o   Control

o   Growth

o   Reproduction

o   Excretion

o   Nutrition

·        If something does not carry out all of these life processes, it is either dead or non-living.

·        Viruses are a good example of non-living particles.

Nutrition

·        Organisms must obtain food to provide energy.

o   Energy is necessary to carry out life processes e.g. Movement, respiration and excretion.

 Nutrition in 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.

Nutrition in 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.

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

Excretion

• Chemical reactions that take place inside living cells are described as metabolic reactions

• Metabolic reactions produce waste products, some of which may be toxic

• These toxic products must be eliminated from the body

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

Excretion in 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

Excretion in plants

• Waste products excreted by plants include:

  • Oxygen from photosynthesis

  • Carbon dioxide from respiration

  • Water from respiration and other chemical reactions

Response to Surroundings

• 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 chance of survival

Sensitivity responses in animals

• In humans, the nervous system provides a complex system of receptors, neurons, and effectors that 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

Sensitivity responses in plants

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

  • Geotropism describes a plant's response to gravity which causes the roots to grow down into the soil

  • Phototropism describes a plant's response to light which causes shoots to grow toward sunlight

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

Control

• Living organisms must control their internal environment in order to keep conditions within required limits

• This is called homeostasis

Homeostasis in 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)

Homeostasis in plants

• Plants use transpiration to maintain a suitable temperature

• Water evaporates from the stomata on the underside of the leaf, leading to heat loss

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 and asexual

Sexual Reproduction

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

  • In humans, the male gamete is the sperm and the female gamete is the egg

  • In plants, the male gamete is in the pollen grains and the female gamete is in the ovule

• The DNA of the offspring is composed of both maternal and paternal DNA

Asexual reproduction

• Cells or whole organisms can also reproduce using asexual reproduction

• Mitosis is an example of asexual reproduction

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

• The DNA of offspring is identical to parental DNA

  • Plants can reproduce asexually through tubers, budding, or runners

  • Single-celled organisms such as bacteria or amoeba reproduce asexually

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