Seven Life Processes

The seven processes of life are the key to all living organisms: these processes consist of nutrition, growth, movement, respiration, reproduction, sensitivity and excretion. Although, they may be achieved in different ways depending on the organism. These processes happen with in both plants and animals; in each organ, cell and organelle. All these processes are interlinked and have a chain effect upon one another. Without one of them the others aren’t possible.

Movement
For living things to find energy/nutrients they have to interact with their surroundings, this is only possible if movement is able to happen. A plant will turn its leaves to the sun (phototropism): strands of xylem and phomen provide a skeleton like structure for the plant to grow towards the light source. Whilst a plant’s roots grow downward in response to the pull of gravity known as gravitropism.

Nastic movement in plants do not involve growth and do not depend on the direction of the stimulus. The leaflets of a Mimosa Pudica, after being exposed to thermal stimuli through touch react due to the change on turgor pressure within the base of each leaflet. It can take only a few seconds to cause a response. Another nastic response is sleepmovement, known as photonasticy, a plant’s response to night and day. This again is a reaction from the change of turgor pressure in motor cells.

Active transport is an example of movement on cellular level as only take place in a living system that is actively producing energy by respiration. Energy is needed for the molecules or ions to be carried against their concentration gradient. (M.B.V. Roberts, Biology a functional approach)

Animals have the ability to move from one place to another. This occurs in three different environments, water, land and air; in basic terms it enables them to move away from danger and find food.

In water, buoyancy reduces the influence of gravity. The primary force restricting forward movement is drag, so the body shape of the organism is important in order to reduce the friction and turbulence created through swimming. The sinuous undulation of an eel’s body propels it forward as each body segment pushes against the water and the moving wave forces the eel forward.

On land, vertebrates and arthropods have been able to develop the means of rapid locomotion across a surface. Both of these body groups are raised above the ground by a series of jointed appendages, the legs, and can move forward by pushing against the ground. Not only do the legs provide propulsion but also support for the body, providing it with stability, helping the body maintain its centre of gravity when moving.

In the air, flight is achieved by birds and insects by pushing down against the air with their wings. This raising and lowering of the wings happens due to the alternating contraction of the extensor muscles known as the elevators and the flexor muscles, the depressors. In flies and insects, the movement of their wings are too rapid for nerves to carry successive impulses. So in order for this to happen flight muscles are not attached to the wings, but to the stiff wall of the thorax, that becomes distorted in and out by the movement. The result of this distortion triggers its contraction in turn without the arrival of a nerve impulse. For example, a mosquito can beat its wings more than 1000 times per second.

Respiration
Respiration is a chemical change carried out in all living animals and plants, and is a continuous process. Not all animals respire in the same way, but in all cases they consist of numerous flat surfaces, sacs or tubes, with a large surface area. For instance earthworms exchange gases across the entire surface area of the body, flatworms are the same but through having a flattened body the surface area not only maximises respiration but also decreasing the distance in which diffusion has to occur within the body of the worm. External gills are another way of increasing the surface area for respiration an example of this can be found on a lugworm where respiration occurs not only in the gills but across the body surface. Internal gills within a fish are highly vascularised, a ventilation mechanism in this case the opening and closing of a fishes mouth, drawing the water through the gills. Within arthropods gas is exchanged at the terminal ends of the tracheal tubes that spread throughout the body penetrating all the tissues.

In larger animals, especially active ones, the surface volume ratio is too small, expansion of the thorax draws air down the respiratory tract into the lungs. The lungs consist of tree like structure made up of bronchioles spreading throughout the lungs with each one ending with alveoli. It is here that gas exchange takes place through the alveolar membrane, a very thin barrier only 0.3 (.m thick in its thinnest part, reducing resistance to enable easy diffusion into the bloodstream. Within humans two lungs contain approximately 700 million alveoli giving it a total surface area of over 70 sq meters, giving the lungs an enormous surface area for gas exchange to take place in.

Looking at respiration on a cellular level it involves metabolic reactions that use energy from carbohydrates, fatty acid, and amino acid breakdown all to produce ATP molecules. It is a process that requires oxygen and gives off carbon dioxide and is known as aerobic respiration. It usually involves the complete breakdown of glucose to carbon dioxide and water. This process takes place within Mitochondria for both plant and animal cells.

In animal cells glucose molecules are high energy are high energy whereas the breakdown products, carbon dioxide and water are low energy therefore energy has to be released. The carbon dioxide and ATP are then transported out of the Mitochondria and into the cell’s cytoplasm where the ATP is then ready to be used elsewhere. The carbon dioxide diffuses out of the cell through the plasma membrane and into the bloodstream to be carried to the lungs where it can be exchanged. The water can either remain in the cell, be diffused into the blood or excreted by the kidneys if need be or released by homotherms as a way of maintaining body temperature through sweating.

In plants aerobic respiration occurs in the opposite direction to photosynthesis. As photosynthesis builds up sugars at the same time respiration is using them up, unlike photosynthesis it is an on going process.

In anaerobic respiration oxygen is not present, and the glucose molecules are only partly broken down so instead of the end product being carbon dioxide and water it is lactic acid or ethanol depending on the nature of the organism. Within the animal world it is lactic acid that is produced during vigorous exercise when the heart and lungs are not able to supply enough oxygen to the muscles. This form of respiration is not as efficient as aerobic respiration as only a small amount of energy is released due to the glucose only being party broken down. So in terms of energy production anaerobic respiration would be an insufficient process if it were carried out continuously. However during exercise it is extremely useful as the lactic acid produced can be broken down or converted into carbohydrate using the Krebs cycle when oxygen becomes available.

In plants, ethanol that is the product of anaerobic respiration, and unlike humans with lactic acid, it is not possible for ethanol to be converted into carbohydrate or be oxidised. As ethanol is toxic to plants it cannot accumulate, in order to stop this from only plants can only respire anaerobically for short periods of time. An example of this is during seed germination, but before the concentration of ethanol gets to high anaerobic respiration must stop and the plant will revert back to aerobic respiration.

Reproduction
Every type of organism can make more or another like itself like its self. There are two different ways in doing this: sexually and asexually.

Sexual reproduction involves meiosis, gamete formation and fertilization resulting in offspring being produced with inherited chromosomes from each parent creating a unique combination of genes allowing genetic variability and in a changing environment contributes to evolution. Gametes are haploid, it is not possible for them to develop unless they fuse properly this is known as synagmy. Gametes that differ in shape size and behaviour are known as heterogametes. An example of heterogametes is eggs and sperm with synagmy taking place during fertilization. After many cell divisions an embryo develops for example into a specific type of whale or a flower due to the blueprint, or nucleic acids, deoxyribonucleic acid (DNA) or sometimes ribonucleic acid (RNA). It is these complex molecules that are present in all living organisms. Gametes contain one set of chromosomes, while a zygote is a diploid and contain two sets. It takes two distinct gametes, formed though meiosis, to form a zygote.

With human reproduction the gametes involved are sperm and eggs. Often the male gamete is called the spermatozoon and usually has a flagellum. Whereas the female gamete is known as the ovum and is produced in the ovaries, unlike the spermatozoon in nonmotile and is larger than the male gamete. There are two different types of fertilization; external and internal. In human reproduction it is internal fertilization that takes place. The spermatozoon has a head, neck, middle piece, tail and end piece. Within the head is the nucleus where the DNA is held, as it is a haploid it only contains half the number of chromosomes, the other half is in the egg. The tail is used for propulsion to swim. Surrounding the axial filament that runs the full length of the tail are densely packed mitochondria, rich in respiratory enzymes providing the energy enabling the spermatozoon to swim.

External fertilization is where eggs are fertilized outside of the body, an example of this can be found in fish when the male deposits sperm into a body of water and they travel until they reach an egg or eggs that have been deposited into the water by a female. Internal fertilization is where the sperm is deposited into the female egg within the reproductive tract.

Like animals, plants contain ovaries within their flowers, some may only contain one but it is here that the haploid egg cell is found within an embryo sac. The male part of the flower is the known as the anther, it is here that the male gametes are made through meiosis in the form of pollen. When the grains of pollen are mature the anther dries out and a process called dehiscence occurs where the anther splits and the pollen is released. If pollination is to occur the pollen needs to land on a compatible stigma here a pollen tube will grow so that the haploid within the embryo sac can be fertilized, creating a diploid zygote that then goes through the process of mitosis and divides many times to produce an embryo.

Asexual reproduction does not involve fusion or the manufacture of gametes from two parents. Every asexual organism can reproduce on its own, this means that every new organism produced this way is genetically identical to the parent, resulting in no variation. This can be useful in agriculture and horticulture but has some disadvantages as it can not adapt to a changing environment or evolve defences against a new disease, therefore m any asexually reproducing organisms can reproduce sexually as well.

Some species of plant’s stems arch and take over a new root at their tips; a good example of this is a strawberry plant. The staolon of the strawberry plant produce new daughter plants at alternate nodes, rhizomes, bulb, corms and tubers are used for asexual reproduction underground and also for food storage (Mader, Biology, 508).

Leaves provide another site for reproduction when mitosis occurs at meristems long the leaf margins of the Bryophyllum plant. Tiny plantlets are produces that then fall off to take up their own existence.

Within the animal kingdom asexual reproduction doesn’t take place on a large scale due to homozygosity. Various methods of asexual reproduction include budding, parthenogenesis, gemmules and polyembryony. Budding is when offspring develop as a growth of the parent. This is true to jellyfish; hydra cells within the organism split into parent and daughter cells. The process starts with the formation of a small bud on the side of the body, as it enlarges it develops tentacles and eventually drops off. Corals on the other hand do not drop off; they stay as attached to form colonies.

In parthenogenesis females produce eggs that then go on to develop without getting fertilized this can be found in some species of fish frogs and insects. Flatworms reproduce by the means of gammules. This involves cell masses being released from the organism. And finally olyembryony is when a large number of propagules are produced within the creature and then released to enter the next phase of their life cycle.

Excretion
The removal of toxic waste from plant and animal cells caused by the high number of metabolic reactions carried out in the organisms is known as excretion. These reactions include aerobic respiration (producing water and carbon dioxide), anaerobic respiration (producing lactic acid or ethanol and carbon dioxide), dehydration synthesis (producing water), protein metabolism (producing nitrogenous wastes) and other metabolic processes that can produce salts, oils, etc. Different species of animals have different means in which the go about this process. Fresh water flatworms are equipped with two strands of branching tubules that open to the outside of the body by pores, situated within the tubules are flame cells that flicker, propelling excess water and waste products out of the body. There are many other excretory systems in small organisms such as nephridra in earth worm and malpighian tubuoles in insects.

The main excretory organs within higher animals (mammals and other vertebrates, regarded as having relatively advanced characteristics) are lungs, liver, skin and kidneys. Lungs are responsible for the excretion of carbon dioxide and water, the waste products of cellular respiration are removed as gasses through respiration, and this is done through exhalation of the lungs. The liver is the largest organ in vertibrates, and is known for its multipurpose qualities. It changes the haemoglobin of worn out red blood cells into bile pigments, bilirubin and biliverdin. These pigments are then passed into the alimentary canal to be excreted within faces. It is also here where the conversion of ammonia into urea takes place and is then excreted through urine as uric acid.

This evaporates and cools the body. When the kidney fails urea is excreted by sweat glands. The skin excretes through sweat glands, these sweat glands produce a solution consisting of water and salt, this evaporates and cools the body, and is a vital part of temperature control within the organism. Small amounts of other metabolic waste products are collected from around the body and sent to the sweat glands for excretion transported via the bloodstream, urea being one of them. Kidneys are a pair of organs found in vertebrates, used for regulating the chemical composition of the blood and are the site for the production of urine. Urea is created within the nephrons of the kidneys; from here it is transported to the glomerular capillaries where the filtration of the urea takes place through its semipermeable walls.

Unlike animals, plants do not have any specific excretory organs, but excretion still takes place, in the stomata of the leaves and the lectins of stems ridding the plant of gaseous wastes consisting of carbon dioxide and oxygen that are produced through respiration and photosynthesis. Another way in which a plant can excrete products of metabolic reactions is through storage within leaves and bark, when the leaves and bark are shed the harmful toxins are eliminated. An example of this is tannin stored within the bark.

Nutrition
Nutrition is the process of providing or obtaining the food necessary for health and growth. Compared to the simple nutritional requirements of plants, an animal’s requirements are more complex.

An animal that feeds on solid organic material must have the means of obtaining it and be able to break it down into a suitable substance for ready for absorption within the body. And like wise with in a plant the conditions must be correct too.

There are different types of nutrition across the animal and plant kingdom, autotrophic, heterotrophic, saprotropic, parasitic and holoztic. However I am only going to be concentrating on two. Autotrophic can be known as self feeders such as algae, these feed on their own food out of raw materials. Where as heterotrophs need a source of organic nutrients. Within this category there are herbivores, animals that directly graze on plants. Omnivores, that feed on both animals and plants and Carnivores that feed only on other animals. The nutrients that are required by animals include carbohydrates, lipids, nucleic acids, proteins, minerals and vitamins.

Up to two thirds of an animal’s daily calorie intake is from carbohydrates, making them the basic source of energy for all animals, that have to obtained form their external environment. Whereas plants synthesize carbohydrates during photosynthesis. Lipids are used for the formation of some hormones, the sheaths surrounding nerve fibres, cell and organelle membranes. The fats are also a useful energy source. During the digestion process nucleic acids are broken down into nucleotides and are the ready to be absorbed into the cell, where they are used for the construction of deoxyribonucleic acid and ribonucleic acid (DNA and RNA).

Proteins are made up of 20 kinds of amino acids, many can be synthesized, but others need to be supplied through diet where they are broken down into their constituent amino acids during digestion. On a cellular level they are essential within the cytoplasm, membranes and organelles, not only are they needed in cell structure they are major components of muscles ligaments and tendons.

Animals tend to acquire the minerals they need through the consumption of plants, these minerals include sulfur, potassium, phosphorous, zinc and magnesium. Vitamins are required to do different jobs around the body and are only needed in trace amounts, they can be water soluble or fat soluble. For good vision vitamin A is needed, vitamin B is used in cellular respiration and vitamin D helps assist in the absorption of calcium.

Carbon, hydrogen and oxygen are the three of the elements that make up 95% of the dry weight of a flowering plant and are taken from the air and water. The absorption of chemicals from the soil via the roots provides the remaining 5%. In total there are 17 essential inorganic nutrients, or elements, including carbon, hydrogen and oxygen some of the essential nutrients that are needed more than others are known as macronutrients and those that are needed in smaller amounts are referred to as micronutrients but are all needed in specific amounts. The macronutrients absorbed from the air are oxygen, carbon, and hydrogen.

The ones that are obtained through the soil are nitrogen, potassium, magnesium, phosphorus, calcium and sulphur. No micronutrients are obtained through the air, only the soil, and these consist of iron, boron, chloride, manganese, zinc, copper, molybdenum, and nickel. Green plants obtain energy through the process called photosynthesis in order to build up sugars from carbon dioxide and water using sunlight as the source of energy, this type of nutrition is known as autotrophic. However plants can also be Hetertrophs and are known as carnivorous or insectivorous plants, all these plants have green leaves and obtain their carbohydrate by photosynthesis but nitrogen from the bodies of their victims. They attract their insect by their colour, scent of sugary bait. When trapped they are then killed and digested by fluid produced by the plant that is rich in protease. The Venus fly trap is a wonderful example of this.

Growth
Both plant and animal organisms grow. Plants however continue to grow throughout their lifetime, whereas animals stop once they have reached adulthood.

It is a gradual increase in size that is aquired by an organism in the course of its development. During the course of its life there are three main processes that contribute to growth cell division, assimilation and cell expansion. Cell division within multicellular organisms is the basis of growth in order to grow to the size of the parent cell. For this to happen the daughter cells must be able to manufacture new structures from the absorption of raw materials from their surroundings. This is known as assimilation and results in the expansion of cells. Within plants growth is aided by the uptake of water through the process of osmosis into vacuolated cells causing the cell to expand like a balloon, this can result in rapid elongated of the stem. One example of where this happens on a plant is within localized regions in the plant called meristems, the site on a plant where new shoots form.

Growth in both plants and animals tends to be regulated by hormones, all stages of life. In plants growth is controlled by hormones known as auxins. In mammals the hormone most commonly involved is secreted by the pituitary gland and carried through the bloodstream directly to the epiphyses within the bones and to other sites where growth is taking place. During adolescence the rate of growth is increased due to the pituitary gland producing an abundance of growth hormones resulting in a growth surge.

Sensitivity
All organisms react to stimuli, ranging from a plant growing towards the sunlight to the rapid withdrawal of one’s hand from a hot object. Plant react to fewer stimuli than animals, gravity, water and light are the main stimuli but also changes in temperature, chemicals and touch. Usually a plant will respond gradually by a altering its direction of growth or rate of growth. These slow movements are referred to as tropsims, and are controlled by chemicals called plant growth regulators. An example of this can be seen over the course of the day in a sunflower, as it tracks the movement of the sun. In the morning the flower head face will face east and by sunset it will be facing west. This happens as the chemicals within the stem cells shift from one side to the other, resulting in movement. The influence of light effects how shoots grow, they bend towards it maximising photosynthesis. Roots will grow downwards to seek out water and also because of Gravitropism (the effect of gravity).

Temperature and the water content of the soil will affect when seed germinate. For example the change in temperature and light for the Forsythia plant results in a change in auxin flow, causing the elongation of cells breaking the connection between the layers of cells, allowing the leaves to fall off the plant. In animal organisms external conditions stimulate the nervous system happens through a chain of events starting with a receptor. This receptor may be eyes (light), ears (sound), taste (chemicals in foods) touch which is usually through the skin (pain, heat, cold, pressure) and the nose (smell).

An animal’s response to stimuli, such as light, sound and scent tends to be rapid and can be essential to its well being and survival. If you were to hit your finger with a hammer the touch receptors will respond, (pain and pressure) an electrical signal will be transmitted to the through the nervous system to the brain. Here the signal is interpreted causing a response to address the stimulus. In this case withdrawal of your finger.

The nervous system includes sensory receptors, sensory neurons, and motor neurons. Sensory neurons are activated by a change in the external or internal environment know as the stimuli. This is then converted to an electronic signal that is transmitted to a sensory neuron, which then connects to the sensory receptors in the central nervous system (CNS). The CNS processes will then process this information and send a signal to the effector organ through a motor neuron, causing the organ to respond in the correct manner. This is referred to as a reflex arc.

This relationship between the sensory and motor neurons is a reflex; a reflex is quick due to only a few neurons being involved. Somatic reflexes are when the result is the contraction of skeletal muscle, whereas autonomic involve the activation of smooth and cardiac muscle. An example of this is an increase in heart rate. Although these reflexes are different they have the same five basic elements: receptor, sensory neuron, integration center (the CNS), motor neuron and effector.

To conclude, all living organisms display the seven signs of life: all living things ingest substances, grow even when fully mature, move, respire and reproduce; they are all sensitive to their environments and excrete waste matter.

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Sylvia S. Mader, Biology (Mc Graw. Hill 8th edition 2004)
M.B.V. Roberts, Biology a functional approach (Nelson 4th edition 1986)