Chapter 2 Flashcards
How do I know what’s alive?
My attempts! How do I know I am alive? I eat, breathe, am aware of myself, I move. How many life forms on Earth? Hundreds of thousands of different species. All life forms have four characteristics in common: what do you think they are? Generate energy, have at least one cell, excrete, have a nervous system. All life forms are made up of something. What is it? Matter.
What is biodiversity? How many life forms are out there?
Biodiversity refers to the diversity of living organisms. There are over 1.5 million officially registered life forms or types of organism, known in biological terms as a species, of animals, plants and fungi living on Earth (excl. bacteria; viruses are different kettle of fish!). Estimates as to the actual number of species cover a vast range upwards of 3 million. In 2011, scientists estimated that there were 8.7 million, but 2016 studies suggest this number could exceed 1 trillion.
What is an organism?
An organism can be simply defined as an individual living thing.
What is a kingdom?
A kingdom is a group of species which all have certain fundamental characteristics in common.
How many species predicted by mathematical modelling?
animals: 7.77 million (12% described and named)
fungi: 0.61 million (7% described and named)
plants: 0.30 million (70% described and named).
What is taxonomy?
The ranking or organisation of living things is known as taxonomy.
What is a taxon and what is the plural?
Taxon is a group or a rank within a taxonomic scheme.
What is a domain? Who introduced the 3 domain system, what is it and what characteristics is it based on?
The top taxon is called a domain. Carl Woese introduced the 3 domain system in 1990 which became the most generally accepted one. The three-domain system is based on genetic differences between life forms found in each domain and the domains are called Archaea, Bacteria and Eukarya.
Archaea
Archaea are classified as prokaryotic based on their physical structure (i.e. they do not have internal cellular compartments). However, they do have similarities with eukaryotic cells on a genetic level. Based on these characteristics, Archaea are classified in their own domain.
Bacteria
The Bacteria domain is comprised of prokaryotic cells. Prokaryotic cells do not have separate internal compartments.
Eukarya
The Eukarya domain is composed of eukaryotic cells. Eukaryotic cells have their internal contents packaged up within compartments in the cell.
Prokarya v Eukarya
Both have cell membrane and genetic mat. Pro doesn’t have nucleus or internal compartments.
Humans: tree
eukaryote animalia chordate mammalia primate hominids homo sapiens
Tree!
Domain Kingdom Phylum Class Order Family Genus Species
What are the domains?
All of ‘life’ is classified into three domains: Archaea, Bacteria and Eukarya. Humans are part of the Eukarya domain.
What is a kingdom? How many are there?
The second highest taxonomic rank for living organisms is kingdom. It is generally accepted that there are six kingdoms. Organisms are placed into kingdoms according to their ability to make food and their cellular structure.
The Archaea domain consists of one kingdom, Archaea also called Archaebacteria. The Bacteria domain consists of one kingdom, Bacteria. The Eukarya domain consists of four kingdoms: Animalia, Plantae, Fungi and Protista.
Humans are part of the Animalia kingdom.
Phylum.
The third taxonomic rank for living organisms is phylum. The animal kingdom consists of approximately 35 phyla and plants have about 12 phyla. It is not possible to give an approximation for the number of phyla for the other four kingdoms. Humans are classified in the ‘chordata’ phylum. All chordates have a backbone at some point in their life.
Class.
The fourth taxonomic rank for living organisms is class. Mammalia is a good example of an animal class; humans are mammals and belong to this class.
Order.
The fifth taxonomic rank for living organisms is order. Humans are part of the ‘primate’ order, which means ape-like animals, in the animal kingdom.
Family.
The sixth taxonomic rank for living organisms is family. There are specific rules for determining whether a species is a member of a specific family. Humans are classified as ‘hominids’ or ‘human-like animals’.
Genus.
The seventh and penultimate taxonomic rank for living organisms is genus. In binomial nomenclature the genus name is the first part of the species name. The binomial name for humans is ‘Homo sapiens’; ‘Homo’ is the genus name, meaning ‘humankind’. It is important to note that the binomial name is written in italics and the first name has an initial capital letter.
Species.
The final taxonomic rank and the basic unit of biological classification is species. All species have a Latin or ‘binomial’ name which is written in italics. The first part of the name should have a capital letter at the start of the word and the second part of the name is in lower case. Homo sapiens are ‘modern humans’, although ‘sapiens’ means ‘capable of discerning’ or ‘wise’, so one could say that Homo sapiens means ‘wise humankind’.
Linnaeus.
In 1735, Carolus Linnaeus, a Swedish botanist (‘plant biologist’) and zoologist (‘animal biologist’), classified over 10 000 plants and animals and described them in his publication Systema naturae. Linnaeus realised that there had to be an organised and systematic method of naming the animals and plants described, so he developed the naming system for living things which we still use today. The reason that the naming system is vitally important is so that the same name can be used for the same type of living organism wherever it may be in the world, regardless of the local language or common names used.
Binomial system.
The system of naming species is known as the binomial (two-name) system and the language used is mainly Latin. The two parts of the binomial system are the genus and the species. The convention for the binomial name is that it is always written in italics with an initial capital letter for the genus and an initial lowercase letter for the species.
Bacteria.
Prokaryotic - Single Cell. Bacteria are microscopic organisms, generally single cell (unicellular), and are believed to be among the first life forms to inhabit Earth. There are fewer than 10 000 species of bacteria classified but estimates of the actual number of bacteria species range from 10 to 7 to 10 to 9. A gram of soil contains 40 million bacterial cells/ There are approximately ten times as many bacterial cells on the surface of a human body as human cells inside the human body.
Five groups: spherical, rod, spiral, comma and corkscrew.
Bacteria are also classified by a staining technique known as ‘Gram staining’. Gram staining uses a chemical called crystal violet which is taken up by Gram-positive bacteria (bc thicker cell wall) making them appear dark blue or purple in colour; Gram-negative bacteria do not take up crystal violet stain and appear red in colour.
Escherichia coli: rod-shaped and Gram-negative. Some strains cause disease, such as respiratory illnesses, sickness and diarrhoea, but most strains are harmless.
Archaea.
Neither Prok nor Euk. Archaea (singular: archaeon) is the most recently recognised kingdom. The classification of Archaea as prokaryotic or eukaryotic is the subject of intense debate because Archaea have features that are very similar to bacteria. Archaea are single cells and can be rod-shaped, spherical and many other weird and wonderful shapes. They tend to live in the most inhospitable parts of planet Earth which explains their relatively recent discovery. Archaea can be autotrophic or heterotrophic and seem to thrive in extreme environments. They are found in deep sea rift vents where temperatures exceed 100 °C and hot springs. They are also found in environments lacking in oxygen, such as mud in marshes and in ocean floors, in very salty water and even in petroleum deposits underground. Some Archaea produce the smelly gas, hydrogen sulfide, which can be characteristic of sulfur-rich environments such as Yellowstone National Park in the United States of America.
Protista.
Eukaryotic - single/multi-cell. Protista (singular: protist) are a large and very diverse group of organisms and include around 200 000 species such as slime moulds and Euglena. The designation of Protista as a separate kingdom is a matter of debate because of the diverse nature of the species within the kingdom. Protista can be defined as eukaryotic, single-cell organisms that are not plants, animals or fungi. However, they can display animal-, plant- or fungus-like characteristics. Some Protista are autotrophic, creating their food from the energy in sunlight, and others are heterotrophic, ingesting their food stuff. You can see why Protista are such a difficult group to classify!
Plantae.
Eukaryotic - multi-cell - autotrophic (photosynthetic)
Plants have existed on Earth for millions of years and plants and can be found pretty much everywhere; there are thought to be more than 300 000 plant species.
All green plants, along with algae, some bacteria and some archaea are autotrophs, i.e. capable of synthesising their own food. Plants do this by using sunlight energy in a process called photosynthesis. Plants convert energy from sunlight into food and oxygen. The oxygen is released into the atmosphere and the food is stored within the plant.
Green plants are essential for the survival of animals because animals cannot get energy directly from the sun. Herbivore animals get their energy by eating plants, whilst carnivores eat other animals, which have eaten plants. Animals also need oxygen, produced by plants, in the atmosphere to survive.
Most, but not all, plants are green due to the presence of chlorophyll, the essential pigment for photosynthesis. There are some plant species which are not green and do not make their own food, i.e. they are heterotrophic. The heterotrophic plants can be further divided according to their type of nutrition. Saprophytes are organisms that get their nourishment from dead or decaying organic matter, many fungi are also saprophytic. Parasitic plants live off other living plants to get their nourishment. Carnivorous plants (also called insectivorous) get their nutrition from insects, there are about 450 species of insectivorous plants and the pitcher plant shown in the figure is an example.
Fungi.
Eukaryotic - multicellular - heterotrophic - absorptive nutrition. Fungi used to be part of the plant kingdom and they do have some features in common; many for example live in the soil and they don’t move, but a fundamental difference is that fungi are heterotrophic, unlike most green plants which are autotrophic. Fungi are found everywhere on Earth, from the poles to the Equator and perform the essential role of decomposition, i.e. recycling of nutrients from dead and organic matter by breaking them down. You may well have noticed fungal growth on some of your food products, such as that on the tomatoes shown in the figure below, perhaps after storing your products for a little too long in the bottom of your fridge.
Some species of fungus such as the single-celled yeast are used by humans in bread making and beer brewing, and mushrooms and truffles (which are multicellular) are consumed by humans.
Fungi are also used in medicine; in 1928, Alexander Fleming noted a green mould Penicillium notatum growing in a culture dish of Staphylococcus bacteria. He noticed a clear margin around the mould where no bacteria grew and isolated the substance from the mould that appeared to inhibit the bacterial growth. The substance turned out to be penicillin, an incredible medical discovery and the first antibiotic which revolutionised medical practice.
Animalia.
Eukaryotic - multicellular - heterotrophic - ingestive nutrition. Animalia is a very diverse group of living things. There are approximately 35 phyla in the kingdom of Animalia - scientists cannot agree on exactly how many phyla there should be. Many phyla can be identified in the fossil record from 542 million years ago.
One of the phyla is chordata (from Latin), which includes all animals with a spinal cord or backbone. The non-chordate phyla are animals without a spinal cord, and these represent all of the other animal phyla.
There are a significant number of classes, orders, families and species, making the animal kingdom the most diverse kingdom in terms of the total number of species (more than one million recognised species so far).
Cell characteristics.
Cells are the smallest units of living things that show the attributes of life: reproduction, growth, metabolism and sensitivity.
Which cell type was thought to be the first life form on Earth?
Prokaryotic cells, specifically bacteria.
What size are cells?
Cells are found in an enormous variety of sizes and shapes; they can range from the smallest bacteria with a length of 0.1–10 μm (1 μm is 1 × 10−6 m) to plant cells with typical diameters of 50–100 μm. Human cells typically have a diameter of 10–50 μm.
Function determines shape.
The function of nerve cells is to transmit information around a multicellular organism so the cells have evolved to be long to allow this transmission of information, rather like electric wires transporting an electric current around a house.
Epithelial cells are a group of cells that line the cavities in multicellular organisms, and this one would be found lining the gut. The finger-like projections (known as microvilli) act to increase the surface area of the cell to allow more area for absorption of nutrients into the body from the gut.
The sperm cell has a long tail which allows it to swim.
Cell membrane. Cytosol.
The balloon, or outer boundary of the cell, is called the cell membrane and it is an extremely thin, yet very complex, structure made of phospholipids.
Its main function is to keep the cell contents separate from the external environment and at a fairly constant concentration. The concentration of a liquid is defined as the number of particles within a particular volume.
The cytosol (viscous internal environment) needs to be maintained at a particular concentration to allow metabolism (the chemical processes) within the cell to occur. The membrane does this by restricting the movement of molecules from the inside of the cell to the outside, and vice versa, so effectively acting as a barrier.
What are organic molecules?
Organic molecules are naturally found in all living organisms and systems and are composed of carbon atoms in long chains or rings with other atoms such as oxygen, hydrogen and nitrogen attached.
Components of the phospholipid molecule.
The hydrophobic or ‘water-hating’ end of a phospholipid molecule is made up of fatty acids. In Figure 2.2, these are represented by the black squiggly lines in the yellow background. These hydrophobic ‘lipid’ portions make up the ‘tail’ of the phospholipid. The phospholipid molecules associate together because of the non-polar properties of the lipids, which means that they group together away from the polar water molecules (which you met in Topic 1) in the aqueous environment.
The hydrophilic or ‘water-loving’ end of the phospholipid molecule is made up of phosphate groups, represented by blue circles in Figure 2.2. The phosphate groups associate with the aqueous environment on the outside of the cell membrane as they are polar in nature and hydrophilic. The phosphate groups, or ‘heads’ of the phospholipid, end up in the aqueous environment on the outside of the group.
This ‘bilayer’ (or double-layer with lipids on the inside, phosphate groups on the outside) that acts as a protective barrier to the external environment.
Selective permeability.
The phospholipid barrier is not completely impenetrable as there are ‘pores’ in the membrane which allow transport of substances in and out of the cell. Although most substances cannot cross the cell membrane, it is not a total barrier to the movement of substances. Rather than being completely permeable (allowing any substance to pass through), the cell membrane is selectively permeable which means that it allows only certain substances to transfer through.
Diffusion. Concentration gradient.
Molecules of some substances (e.g. oxygen, carbon dioxide and sodium chloride) move freely from one side of the cell membrane to the other by a process known as diffusion. Diffusion is simply the process by which molecules tend to move from areas where they are plentiful to areas where they are scarce.
The movement of a chemical substance from an area where it is at high concentration to an area where it is at low concentration is a process known as diffusion. The difference in concentration is known as a concentration gradient, and the particles move down the concentration gradient, from high to low. The higher the temperature, the faster the particles move and the faster diffusion takes place.
Osmosis
Water molecules move across membranes by the process of osmosis.
Organelles. What purpose does partitioning serve?
Both prokaryotic and eukaryotic cells have cell membranes, but in eukaryotic cells the contents are packaged up into a number of different compartments known as organelles.
The partitioning enables some cell functions to be restricted to particular parts of the cell. Prokaryotic cells have no such internal organisation – all their contents are mixed together in the internal environment.
What is the difference between Brownian motion and diffusion?
Both Brownian motion and diffusion are processes involving the movement of molecules. Brownian motion is the random movement of large particles whereas diffusion is the movement of molecules down a concentration gradient from an area of high concentration to an area of low concentration.
Passive diffusion across a membrane.
The diffusion of a chemical substance can also occur across a permeable barrier, i.e. one that the substance can pass through freely. The lipid bilayer of a cell membrane is permeable to some small molecules, including gases like oxygen. These small molecules can freely diffuse across the cell membrane whenever there is a concentration gradient. The molecules will move randomly in both directions across the membrane, but the net (overall) movement will be from the high concentration side of the membrane to the low concentration side, down the concentration gradient. This type of movement across a cell membrane is sometimes called passive diffusion because it doesn’t require the cell to expend any energy. Diffusion ceases when the concentration of the molecule is the same each side of the membrane.
Direct v special channel diffusion.
Oxygen molecules can diffuse directly across the lipid bilayer of a cell membrane, but other molecules can only diffuse through special channels in the cell membrane formed by membrane proteins.
Osmosis.
Osmosis is a process that occurs when two different solutions are separated by a selectively permeable membrane, i.e. one that lets some substances through but not others. Water molecules can move freely across cell membranes, but solutes dissolved in the water (e.g. sugar molecules or sodium chloride) may not be able to cross the membrane. Osmosis is the movement of water through a partially permeable membrane down the water concentration gradient from a dilute to a concentrated solution.
Dilute v Concentrated.
A dilute solution (where there is a relatively high concentration of water and a low concentration of solutes). A concentrated solution (where there is a relatively low concentration of water but a high concentration of solutes).
Solution volume change in osmosis.
The volume increases on the left side which started out with the more concentrated solution (more solute molecules and fewer water molecules) and decreases on the right side which started out with the less concentrated solution (fewer solute molecules and more water molecules). This is because water molecules move down their concentration gradient by osmosis from the right side to the left side.
Dehydration.
The salt in the blood becomes ever more concentrated so more and more water is drawn out of the cells. This is also the reason why animals must drink fresh water and cannot drink salty seawater. Dehydration has uncomfortable symptoms like dizziness, fatigue and confusion. Severe dehydration is fatal if not treated.
Application of osmosis for food preservation.
Concentrated solutions of salt or sugar can also be used to preserve foods like meat, vegetables and fruit. When foods are placed in a highly concentrated solution of salt or sugar, water is drawn out of the food by osmosis. Similarly, water is also drawn out of any bacteria contaminating the food, killing them very effectively.
Virtual microscope. What pics does it take.
This virtual microscope is a type of light microscope, where light is shone through the cells so that their features can be seen and imaged. Those images are known as micrographs. There are many other types of microscopes, including those that use electrons instead of light (transmission electron micrograph, TEM); and fluorescence microscopes.
Plant v animal cell.
Both the animal and plant cells have cytosol, mitochondria, a nucleus, nuclear membrane and cell membrane.
Plant cells have chloroplasts, a cell wall and a large vacuole, whereas animal cells do not. The plant cell has a regular shape defined by the cell wall; the animal cell has an irregular shape defined by the cell membrane.
The plant cell is much larger than the animal cell. The scale in the plant cell drawing is 7 μm, whereas it is 1 μm in the animal cell.
Animal cell.
Animal cells are eukaryotic cells surrounded by a cell membrane (plasma membrane). With the exception of red blood cells (erythrocytes), all animal cells have a large organelle called the nucleus, which is surrounded by a double membrane called the nuclear envelope. The nucleus is generally the most prominent feature of a eukaryotic cell. The nucleus contains the hereditary material deoxyribonucleic acid, usually known as DNA, which is packaged into chromosomes. The cytoplasm is the gel-like substance within the cell membrane in which all intracellular organelles sit. The organelles are membrane-bound structures and include mitochondria, endoplasmic reticulum (smooth and rough) and lysosomes. The endoplasmic reticulum nearest the nucleus is studded with ribosomes and is described as rough; while further out from the nucleus is the smooth endoplasmic reticulum, which lacks associated ribosomes. Free ribosomes can also be found in the cytoplasm. The structure and content of a cell depends on its function.
Cell membrane.
The cell membrane (plasma membrane) is the outer membrane of a cell and is composed of a single phospholipid bilayer with proteins embedded in it, although no membrane proteins are shown in this schematic image of a cell. The cell membrane separates the contents of the cell from the outside environment. Particles can be incorporated into the cell by endocytosis, a process by which the membrane invaginates to enclose the substance, then pinches off to form a vesicle that moves inside the cell. In the opposite process, exocytosis, cytoplasmic vesicles fuse with the cell membrane to expel their contents from the cell
Lysosomes
Lysosomes are cellular organelles bound by a single membrane. They are known as the ‘dustbins’ of the cell as they contain digestive enzymes that breakdown unwanted cellular contents such as ‘worn out’ organelles or engulfed bacteria. They are not thought to be present in most plant cells, where the vacuole may perform a similar function
Mitochondria
Mitochondria are often known as the ‘batteries’ of the cell and are found in the majority of eukaryotic cells. They produce the majority of the cell’s stored chemical energy in the form of adenosine triphosphate (ATP). A mitochondrion (singular for mitochondria) has two membranes, the outer membrane and the inner membrane, with the intermembrane space lying between them. The inner membrane is ‘convoluted’ or wiggly in shape
Nucleus.
The nucleus is known as the ‘control centre’ of the cell, it coordinates many of the cell’s activities including protein synthesis, growth and cell division. The nucleus is the largest organelle in the cell and contains the hereditary material, deoxyribonucleic acid or DNA, packed into chromosomes. The nucleus contains a small nucleolus. The nucleus is enclosed by a double phospholipid membrane called the nuclear envelope. The outer membrane has holes known as ‘pores’ to allow transport of large molecules from the nucleus. Immediately outside the nuclear envelope is the rough endoplasmic reticulum which has ribosomes on its outer surface.
Ribosomes.
Ribosomes, which are found in all cells, are complex structures that are responsible for synthesising proteins. Ribosomes are most abundant in the cytoplasm, either free in the cytosol or attached to the rough endoplasmic reticulum (RER).
Rough ER (RER)
The rough endoplasmic reticulum (RER) is an organelle consisting of a network of single membrane-bound tubes that is continuous with the outer layer of the nuclear envelope and which is studded with ribosomes. The ribosomes of the RER are located on the outer surface only, which faces the cytosol. The RER is the site of proteins synthesis, including membrane and lysosomal proteins, and proteins that are to be exported from the cell. The endoplasmic reticulum acts as a ‘transport system’ for eukaryotic cells.
Smooth ER (SER)
The smooth endoplasmic reticulum (SER) is a single membrane-bound organelle. Unlike the rough endoplasmic reticulum (RER), it has no ribosomes attached. The SER is the site of many activities, including the synthesis of lipids. The endoplasmic reticulum acts as a ‘transport system’ for eukaryotic cells.
Plant cell.
Plant cells are eukaryotic cells with several distinctive features that distinguish them from animal cells. Plant cells are surrounded by a cell wall, which is a rigid barrier outside the cell membrane. Plant cells usually have a large central vacuole, a water-filled space enclosed by a membrane. As in animal cells, the chromosomes are enclosed in a nucleus bounded by a double phospholipid membrane called the nuclear envelope. The cytoplasm includes similar organelles to animal cells, including mitochondria and endoplasmic reticulum, but also some other types of organelles called plastids, where molecules are synthesised or stored. Chloroplasts, for example, are plastids that contain chlorophyll, the green-coloured pigment used in photosynthesis. Chloroplasts are found only in plant cells, not animal cells.
Plant cell membrane.
The cell membrane in plants is known as the plasmalemma. It is composed of a phospholipid bilayer with embedded proteins. As in animal cells, it separates the contents of the cell from its outside environment.
Plant cell wall.
Plants (and also fungi and bacteria) have a rigid cell wall structure outside of the cell membrane. Cell walls are composed predominantly of cellulose, which helps to provide shape, mechanical support to the plant and prevents the entry of large molecules that may be toxic to the cell. In comparison, animal cells do not have cell walls. Cell walls are composed predominantly of cellulose.
Chloroplasts.
Chloroplasts are the organelles in which photosynthesis takes place. They are found in the green parts of plants (leaves and stem). Chloroplasts are bounded by a double phospholipid membrane. The green pigment chlorophyll is found in chloroplasts and is essential for the process of photosynthesis. Photosynthesis is the conversion of water and carbon dioxide into glucose and oxygen, using light as an energy source.
Plant ER.
The endoplasmic reticulum (ER) in plants, as in animal cells, is an organelle consisting of a network of membrane-bound tubes and sheets that is continuous with the nuclear envelope. The rough endoplasmic reticulum (RER) is studded with ribosomes. The smooth endoplasmic reticulum (SER) has no ribosomes attached and is more tubular than rough ER, forming a separate network that usually extends throughout the cytoplasm. The endoplasmic reticulum acts as a ‘transport system’ for eukaryotic cells.
Plant mitochondria.
Mitochondria in plants, as in animal cells, are the cell organelles that produce the majority of the cell’s form of stored chemical energy, adenosine triphosphate (ATP). A mitochondrion has two membranes, the outer membrane and the inner membrane, with the intermembrane space lying between.
Plant nucleus.
In plant cells, as in animal cells, the nucleus is the large organelle that contains the hereditary material, DNA, packed into chromosomes. It coordinates many of the cell’s activities including protein synthesis, growth and cell division. The nucleus contains a small nucleolus. The nucleus is enclosed by a double phospholipid membrane called the nuclear envelope. The outer membrane has holes known as ‘pores’ to allow transport of large molecules from the nucleus. Immediately outside the nuclear envelope is the rough endoplasmic reticulum which has ribosomes on its outer surface.
Plant ribosome.
Ribosomes, which are found in all cells, are complex structures that are responsible for synthesising proteins. Ribosomes are most abundant in the cytoplasm, either free in the cytosol or attached to the rough endoplasmic reticulum (RER).
Vacuole.
A vacuole is a cell organelle that is very prominent in plant cells. A vacuole is enclosed by a membrane and filled with water, ions and small organic molecules. Most mature plant cells have a single large vacuole which has several roles. Firstly, it helps to maintain the internal hydrostatic pressure, or turgor, that maintains the cell shape and which plants rely on to remain upright and support important structures such as leaves. It is also involved in the storage of some chemicals and has a similar disposal role to that of the lysosome found in animal cells.
Hormone
Hormone – a signalling molecule within a multicellular organism; effectively hormones deliver messages between cells.
Arthropods
Arthropod phylum. Arthropods do not have a backbone, i.e. they are ‘invertebrates’. They have an exoskeleton, a segmented body with jointed legs and are symmetrical along their length. Arthropods include classes of: insects (butterflies, ants, etc.), arachnids (spiders, mites, scorpions, etc.), chilopods (centipedes) and diplopods (millipedes).
What are the three processes involved in growth?
Cell division, synthesis of new structures from raw materials and cell expansion.
What sort of growth pattern do vertebrates show?
Slow, fast, slow as adulthood reach.
What sort of growth pattern do arthropods show?
Unlike other invertebrate, arthropods do not increase slowly and gradually over time. They grow in steps and must shed their exoscheleton to do so. Mayflies shed 50 times and are the only ones to do so after getting their wings.
What are meristems and where are they found?
Meristems are actively dividing cells found in plants at the tips of roots and shoots.
What factors determine growth in plants and animals?
External factors include temperature, diet and light. Growth is determined internally by hormones.
Why don’t cells just grow by getting larger?
This would result in very large cells which would become unsustainable. The maintenance of the cells (e.g. regenerating tissue and regulating the internal chemistry through homeostasis) would be too energy intensive. As a result, the intracellular functions would become compromised as the energy required for homeostasis and repair became too great.
Secondary growth
Growth in trees takes place in both the stem and the roots by the division of meristematic cells located in the vascular part of the plant.
Cell division.
Cell divisions and growth cycles. Each cell produces two progeny cells when it divides. These grow and then divide in turn. This mechanism of cell reproduction to enable growth allows the replenishment of worn-out cells as well as the overall growth of a multicellular organism.
Mutation.
Both prokaryotic and eukaryotic cells reproduce by copying their chromosomes (which contain their DNA) and passing on an identical copy of their genetic material to each progeny or ‘daughter’ cell. Occasionally the reproduction of chromosomes is not completely accurate – when mistakes occur the process is known as mutation.
