Biology – Module 2 – Patterns in Nature

  1. Plants and animals have specialised structures to obtain nutrients
    from their environment.
  • identify some examples that demonstrate the structural and functional relationships between cells, tissues, organs and organ systems in multi-cellular organisms

There are a vast array of cells in our bodies, and each type has its own specific function. A group of cells that perform the same function is known as a tissue, a group of tissues that perform the same function is known as an organ, and a group of organs that interact in order to carry out a function is known as a system.
Different cells have different purposes, such as cells involved in the exchange of substances have special features in order to increase their surface area to volume ratio, allowing them to function more efficiently. For example:

- cells may be flattened (eg. In tissue lining of the airs sacs in the lungs)

- the exposed edges of the cell may be folded, eg. Root hair cells that absorb water and mineral salts in plants.

Cell differentiation and specialization – In multicellular organisms, different types of cells (tissues) are created specifically so that they carry out different functions.

Young cells (called embryonic cells) divide and five rise to new cells. When these cells become specialised to perform a particular function, they are said to differentiate. Once they have specialised to form a particular type of tissue, differentiated cells will lose their capacity to develop into other types of cells.
Undifferentiated cells that are able to divide into other types of cells are informally known as stem cells.

A group of cells that is similar in structure and works together to carry out a common function is called a tissue. Just as similar specialised cells that perform a common function are arranged together to form tissues, so groups of tissues collectively form organs.

An organ is an arrangement of different types of tissues, grouped together for some special purpose; for example, the leaf is an organ for making food in a plant and the heart is an organ for pumping blood in animals.

A system is a collection of organs that all work together to achieve an overall body function, for example the digestive system or nervous system in animals and the transport system in plants or animals.

A multicellular organism is a living plant or animal composed of many systems which function together co-operatively to ensure its survival. When one or more of these systems malfunctions, the organism is no longer healthy and disease or even death may result.

  • distinguish between autotrophs and heterotrophs in terms of nutrient requirements

Living organisms need to obtain nutrients in the from of organic nutrients such as glucose, amino acids, fats, glycerol, vitamins, nucleotides as well as inorganic nutrients such as minerals and water.

Organic nutrients are the main supply of stored energy in living things but are also used in the structures of cells. Inorganic nutrients are essential as structural parts of cells and tissues and they play an essential part in assisting enzymes in reactions but they are not an energy source.

Organisms that can make their own food are called autotrophs. They are able to make their own food by trapping energy from some other system and putting it into simple molecules, which are then made into the sugar glucose. Organisms that trap energy from the sun are said to carry out photosynthesis and those that trap energy from a chemical reaction carry out chemosynthesis.This relies on using energy from breaking chemical bonds to power their food-making, rather than using light energy as do photosynthetic organisms.

Green Plants, cyanobacteria and a small number of other bacteria are photosynthetic autotrophs. Bacteria that make their own food without light are called chemosynthetic autotrophs and they are found on ocean floors where they trap energy from the reactions of the compounds that are released from the cracks in the floor.

All other organisms are heterotrophs. They cannot make their own food and rely on plants or other heterotrophs (that have eaten autotrophs) for their own food. Animals, fungi and most bacteria are heterotrophs.

All living things require energy in order to survive. The energy that is required by all living cells is a type of energy known as ATP (Adenosine Tri-phosphate). The energy of ATP powers all cellular activities. The energy is released when glucose is broken down. This process is known as cellular respiration.

  • identify the materials required for photosynthesis +its role in ecosystems

Requirements for photosynthesis:
Carbon dioxide, water, chlorophyll and light are all essential for the chemical process of photosynthesis.

The water and carbon dioxide which are used by the plant during photosynthesis provide the basic chemical “building blocks” of which the resulting sugar is made. Oxygen is given out as a product as well.
The energy conversion involves a change from radiant energy (sunlight or artificial light) to chemical energy (stored in glucose).

The role of photosynthesis in ecosystems:

Photosynthesis is the initial pathway by which energy enters all ecosystems. Organisms that photosynthesis are producers. These organisms form the basis of all food webs, without them there would be no life as no organism would be able to harness the sun’s energy thus they would all perish. Glucose can be converted by plants into other organic compounds for storage.
Glucose may be converted into and stored as:

  • Lipids ( Sunflowers and Avocados store their food as oils)
  • Proteins (legumes such as beans and peas)
  • Carbohydrates (Potatoes)

These organic compounds, which rely on photosynthesis for their production, provide the structural basis of living cells and also provide a source of energy for all cellular purposes.
Atmospheric gases that are essential to living organisms are recycled during photosynthesis. Eg. The process provides oxygen for the respiration all living things and also removes Carbon dioxide from the atmosphere, thus reducing the effect of the global warming situation.
Furthermore, fossil fuels were formed from photosynthetic organisms approximately 300 million years ago. Large plants were buried and over the thousands of years, as a result of pressure, they turned into coal /oil /natural gas which all serve as sources of fuel for us today.

  • identify the general word equation for photosynthesis and outline this as a summary of a chain of biochemical reactions

The general word equation of photosynthesis:

Light

Carbon Dioxide + Water Glucose + Oxygen

Chlorophyll

Light

6H2O + 6CO2 C6H12O6 + 6O2

Chlorophyll

Photosynthesis can be summarized as a chain of biochemical reactions that take place in the chloroplasts of green plant cells +the cells of some photosynthesising bacteria.
Photosynthesis takes place in two main stages (where each stage is not a singular reaction but rather, it consists of a series or chain of reactions):

-The Light Phase (photolysis) involves the splitting of water using the energy of light

-The Light-Independent phase (Carbon fixation stage) involves using carbon dioxide to make sugar, in the absence of light.

The Light Phase: Light energy from the sun is captured by chlorophyll in the thylakoids in the grana of chloroplasts. The energy is used to remove an electron from a chlorophyll molecule. Once these thousands of electrons have been removed, they can be used for one of two purposes. Firstly, they can be used to decompose water or secondly, they can be used to from ATP.

The Light-Independent Phase: This phase involves the use of Carbon Dioxide. In this stage, the hydrogen atoms (produced during the decomposition of water) are carried to the stroma.

-Carbon dioxide is needed for this reaction and is absorbed by the plant via the air. The hydrogen atoms along with carbon dioxide undergo a series of enzyme controlled reactions to from sugar molecules

-This cyclic cycle as shown in the diagram is known as the Calvin cycle.

-The glucose is then converted into starch which is then stored in the plant.

  • explain the relationship between the organisation of the structures used to obtain water and minerals in a range of plants and the need to increase the surface area available for absorption.

Roots are the structures in plants that absorb water and other inorganic minerals from the Earth. These structures have a significant surface area which allows water and inorganic mineral salts to be absorbed efficiently. The epidermis is the outermost layer of the plants organs and it is through this layer that the transfer of minerals and water will occur.

Plants need to absorb a large amount of water at rapid rates in order to maintain a balance within them. The uptake of water through the roots is through osmosis. Osmosis is typically a slow process but it is speed up in this case due to the large amount of surface area present in the plants root system.

The uptake of minerals through the roots is through diffusion. They are dissolve in water (as they are ions) and they are absorbed by the plant when in this form. Diffusion is too slow to meet the needs of the plant. A process known as facilitated diffusion and active transport is involved, where the plant uses energy to draw in water and mineral ions towards itself.

Increasing Surface Area: The surface area of any root system is multiplied by the factor of twelve due to the presence of root hairs. These microscopic hairs vastly increase the area by which water can diffuse into the plant. Another process can increase the surface area of the root system and this is known as extensive branching. In this case the roots may branch off in one of three ways, thus forming either a tap root system (one main root and then subdivisions occurring from that) or fibrous root system (many branches subdivide).


Root Structure:

The root tip has a root cap which protects the end of the root as it pushes through the soil. The root cap is being constantly worn away and hence is constantly being replaced.

Just behind the root cap is meristematic tissue where cell division constantly makes new cells for growth. Behind this region is the zone of elongation where the new cells get longer causing the root to push out through the soil. Root hairs are produced behind these layers (through the epidermis). Once water is absorbed through the root hair is passed into the xylem in the vascular bundle inside in the center of the root. Inside the xylem, the water travels up the leaves.

  • explain the relationship between the shape of leaves, the distribution of tissues in them and their role

Leaves are the main organ for photosynthesis in flowering plants, although photosynthesis is not restricted to the leaves. Photosynthesis can occur in any green part of a plant. The shape of leaves and the tissues inside the leaf are related to this role of photosynthesis.

A typical leaf has a petiole (leaf stalk) and a flattened blade which is usually thing and broad with a system of veins providing transport for water and sugars. Leaf shape and size for most plants can be related to the native environment of that species. For example plants found in rainforests have large, broad, flat leaves to capture as much sunlight as possible in the light restricted environment, which has plentiful water supply. On the other hand desert plants receive high sunlight but many plants have leaved that have reduced surface area or rolled into cylinders to reduce water loss through transpiration.

Each species has an ordered way in which the leaves are arranged on the stem. This pattern ensures that each leaf receives sunlight so it can photosynthesise. The leaves can be arranged either alternately, opposite or in a whorl.

The upper and lower surface of a lead ha a layer called the epidermis. The epidermis is a transparent layer that allows sunlight to pass through for photosynthesis. Epidermal cells fit closely together to reduce evaporation from the leaf and stop bacteria and fungi from entering. Occasionally, the epidermis is covered in a thin waxy cuticle.

Stomates are found in the epidermis, with more stomata located on the lower epidermis. Each stomate consists of two guard cells and a pore which opens depending on sunlight/water availability.

Mesophyll tissue lies between the upper and lower epidermis. The top zone contains the palisade mesophyll (which contains chloroplast, this is why they are stacked tightly together – so that they can maximize the photosynthesis that occurs). The lower zone contains spongy mesophyll, these are responsible for the gaseous exchange that occurs within the leaf.


Vascular bundles (veins) are also found between the upper and lower epidermis. Vascular bundles contain xylem tissue which delivers water and mineral ions up the plant. Phloem tissue which removes sugars, and cambium tissue which is meristematic tissue with cell division making new xylem/phloem.

The role of leaves:

-to absorb sunlight and carbon dioxide during the day

-to release oxygen

-to provide chlorophyll for photosynthesis

-to make glucose and transport it to other parts of the plant where it can be stored as starch or other organic molecules

-to transpire (release water) in order to cool down the plant and also to create a suction pull to lift water from the roots to the top of the plant.

-To provide a medium for which products / reactants of photosynthesis / respiration can be obtained or released.

  • describe the role of teeth in increasing the surface area of complex foods for exposure to digestive chemicals

Teeth are found in the mouth of vertebrates and are important in mechanical digestion as they break food up into small pieces by biting and chewing. The smaller pieces of food have a greater surface area to volume ratio and this means that digestive enzymes have a greater ability to work effectively. The teeth differ in size, function, arrangement and structure.

Each type of tooth has a specific function. Incisors are chisel-shaped teeth at the front and are used for biting. Canines have a sharp point and are used for tearing meat. Premolars have sharp cutting edges and are used for crushing food. Molars have large flat surfaces with blunt ridges are used for grinding food.

When food enters the mouth, the salivary glands release saliva into the mount chewing mixes the saliva with the food. Saliva has several functions. It dissolves some of the food, helps to lubricate the food and makes some small pieces stick together. Human saliva contains a digestive enzyme known as salivary amylase which splits starch into units of disaccharide maltose. When food is swallowed the acid in the stomach inactivates the salivary enzyme. When the teeth break down the food, they increase the surface area to which the enzyme can get to.

The structure, locations and numbers of teeth can show the diet of a particular organism. For example

Herbivores:have incisors that are used to bite off vegetation. They also have specially adapted molars that are broad and crushing. They are specially equipped with ridges to help break open the cellulose cell walls of plants. It is extremely difficult to break down the cellulose physically or chemically. Furthermore, plants do not provide large amounts of energy for the herbivore, so they must eat for long periods of time. Their teeth are adapted to these situations. Many herbivores have microbes in their gut which increases the rate at which the cellulose is broken. Canine teeth are absent in the herbivore.

Carnivores: They have powerful jaws and well-developed canine teeth, conical in shape and they are specialised for holding and killing prey and tearing meat from the bones. The meat is torn off in chunks and they have molars with large cusps that briefly chew the meat before digestion.

Smaller carnivores (that are adapted to feed on insects) have teeth adapted for piercing and penetrating the tough cuticle of their prey. They have to puncture the exoskeleton with their premolars and then use these teeth to shear the inner tissues.