Answers – Science questions

Section A
1.a. The organelles labelled Y are called Ribosomes, They are attached to the endoplasmic reticulum. The ribosomes make proteins for use in the cell and hold together all components of protein synthesis. The endoplasmic Reticulum spreads all through the cytoplasm and has a large surface area for the attachment of many ribosomes. Also newly synthesised proteins are stored and packaged into vesicles.
1.b. Structure X is called a nuclear pore (A sophisticated entry and exit control system that allows selected chemicals to move into and out of the nucleus, it also connects the nucleus with the cytoplasm). The word pore comes from the Greek word poros, which means Passage. There are around 3000-4000 of them around the nuclear envelope of every cell.
1.c. Cell Functions require energy, the mitochondria is where the energy production takes place. The energy made here is in the form of a chemical named adenosine triphosphate (ATP). The structure of the mitochondria is designed so that it can produce energy for the cell to its best ability. It is a cigar shaped organelle, surrounded by two membrane layers. The inner membrane is folded and forms a structure called a cristae. The organelle has evolved over time to allow for the inner membrane to become further folded to provide greater surface area. This larger surface area allows for more sites of energy production.
In conclusion the mitochondria has evolved over time to accommodate more and more sites of energy production, this means that the cells effectively and efficiently complete their roles within the cell.
1.d. The Nuclear Pore, Ribosomes and the Golgi body work together to make proteins. It all starts at the DNA, this is found inside the nucleus which holds all the important information for the cell. The First step in the process is called transcription, this is where the RNA polymerase unwinds a portion of the DNA strand so it can be read and transcribed. To do this the RNA polymerase attaches to the unravelled section of DNA and reads the code, this then produces the Messenger RNA (MRNA). The MRNA then moves out of the nuclear pore, its purpose is to get the code out of the nucleus without puling the DNA out too. The MRNA moves through the Cytoplasm and attaches to a Ribosome (found either attached to the Endoplasmic Reticulum or on its own in the Cytoplasm). Once the MRNA is attached to a Ribosome, the Ribosome starts to make Transfer RNA (TRNA) which reads the code on the MRNA. This step is called translation, the MRNA is read 3 bases at a time and each section is called a codon. The TRNA’s job is to read the code on each codon and make a specific Amino Acid for each one. The first Amino Acid is brought in by the TRNA and the Anticodon is matched up to the codon on the MRNA. Once the first codon is read the next TRNA moves in and matches up with the next MRNA codon whilst the amino acids form a peptide bond and link together. The previous TRNA detaches and the MRNA shifts for the next TRNA molecule to come in. The protein grows until a STOP codon is reached. Once this happens the protein is formed and ready to finish folding to become functional. After the Protein is functional it is isolated, stored and transferred through the Endoplasmic Reticulum to the Golgi apparatus. The Golgi apparatus Modifies and packages the protein.
1.e. One of the roles of the cell membrane is to regulate materials that pass in and out of the cell. Materials can pass in and out of the cell by diffusion, this is the spontaneous movement of particles from a high concentration to a low concentration. Diffusion does not require energy and takes place with random kinetic movement, it stops when the concentration is equal on both sides (inside and outside the cell). The rate of diffusion depends on a number of factors, the temperature, surface area and the difference in concentration. The cell membrane is selectively permeable, water and oxygen can move freely across the cell membrane. Facilitated diffusion is one of the ways molecules travel through a membrane, this is when a molecule moves through the cell membrane with the assistance of a Protein. An example of diffusion is the movement of oxygen and carbon dioxide inside the lungs. When we breathe in, oxygen enters our lungs and moves into the Alveoli, the oxygen moves through the cell membrane of the alveoli and into the capillary beds. On the other hand Carbon Dioxide, moves from the capillary bed through the cell membrane and into the Alveoli so that when we breathe out Carbon Dioxide is released.

2.a. Blood is a connective tissue. It connects the body systems together taking the needed oxygen, nutrients, hormones and other molecules from one system to another.
2.b. Tissues are a large group of cells all doing the same role inside the human body. Cells do not simply stick together, they are organised into very diverse and highly distinctive patterns. There are four different types of tissues, Epithelial, Connective, Nerve, and muscle tissue. Each tissue has a different role within the body. Epithelial tissues protect the body from infection and injury. Connective tissue supports the body (Bone, cartilage, blood and fatty tissue are within this group). Nerve Tissues connect cells together, impulses pass along the nerve tissues as they collect information from our sensory organs or pass it on to other organs. Lastly is muscle tissue, there are three different types of this tissue; Voluntary (muscles that we move by choice, for example, Biceps, Triceps and gluteus maximus), Smooth (muscles that we do not choose to move for example, muscle in the lungs, stomach and intestines), Cardiac (muscle that makes our hearts).
When cells combine together to make tissues, we then have a group of cells that are all helping each other to perform a task that one cell its own would not be able to accomplish. An example of this is the Cillia
2.c. Blood consists of three different cells, Red blood Cells, Platelets, Plasma and White Blood Cells. These cells work together in transport and defence roles. Below is a picture of each call and how they look in a blood vessel.

Below is a red blood cell, it is made in the bone marrow of some of the bones, including ribs, Vertebrae and some limb bones. It is produced at a very fast rate

Section B
B.1The body’s natural defence mechanisms prevent the entry of potentially harmful pathogens. The primary defence mechanisms role is to be the first line of defence, also known as the outside defence system. It is made up of physical and chemical barricades, it is present and active at all times and is not activated in response to pathogens.
The primary defence has many aspects, these include but are not limited to;
• The skin.
• Tears.
• Mucus.
• Cilia.
• Stomach acid.
• Friendly bacteria.
• Innate immune system/white blood cells.

The skin is the largest organ in the body and is made up of three layers; The Epidermis, The Dermis and the Hypodermis (fat layer). It is arguably the most important barrier as it covers most of the body and it prevents pathogens from entering. The skin is a specialised organ, it not only protects the body but it also senses the environment and helps regulate body temperature. The hypodermis is the deepest layer of skin and it helps store energy and gives the body thermal insulation. The middle layer of skin is called the Dermis and this layer contains sensory receptors, capillaries, muscle, hair follicles, connective tissue, sweat and sebaceous glands. The dermis also helps to give the skin its structure and strength. The outer layer of skin is called the epidermis, new cells are constantly being made and moving upwards towards the surface as dead cells are constantly rubbed off. This process forms a waterproof tough dead surface. Most pathogens cannot penetrate this layer but some fungal infections can grow in it. Cuts, burns and grazes are some of the ways the barrier can be broken, when the barrier is broken it allows pathogens into the body. The skin, when damage occurs, will go through stages to repair itself. Firstly blood enters the wound and forms a blood clot, this is to quickly seal the cut to prevent blood loss and the access of pathogens. At this point a scab will be visible on the surface. Then new skin grows to repair the damage, new skin is sometimes seen as a scar.
Tears, Sweat and saliva are all chemical barriers which contain enzymes that kill pathogens. The chemical barrier, most of the time, destroy pathogens on the outer body surface.
Tears contain a chemical inhibiting bacterial growth called Lysozyme which is also found in Saliva and Sweat. This chemical makes the conjunctiva of the eye mostly free of microorganisms. Also at work is the eye lid, every time a person blinks, it mechanically removes microbes and tears wash the surface of the eye. Sweat Glands produce a combination of Sodium chloride, water and metabolic waste products which inhibit the growth of pathogens. This is a natural antibiotic called Demcidin very effective at fighting bacteria that cause tuberculosis.
Another form of the primary defence system is the cilia, these organelles are a projection from certain cells and they sweep in unison to clear trapped particles from the lungs and windpipe. Dust, smoke, fluid and other particles are some of the things that the cilia help remove or move away from the lungs.
Friendly bacteria grow on the skin, in the mouth, bowel, gut and other places inside the human body. They stop harmful bacteria from taking over and causing infection. Also working to protect us in the digestive tract is stomach acid, this is hydrochloric acid secreted by the stomach lining and the potent acid kills bacteria that can enter within or on the food we eat. Similarly Mucus is found in all wet surfaces of the body for example, the nostrils, lungs and gut. Mucus does not kill pathogens although it does act as a barrier. It engulfs microorganisms and contains proteins that prevent the pathogens attaching to surfaces such as tissues. Also mucus stops microbes from multiplying and forming a cluster formation by keeping the cells separate.
Inflammation is another way in which the body protects us from disease, it can cause warmth, redness, swelling and pain. This occurs when tissues are injured by Bacteria, Toxins and trauma, Cells travel to the site of damage and cause inflammation by releasing chemicals. The chemicals, such as Histamine and prostaglandins, cause blood vessels to leak fluid into tissues causing swelling. This isolates the site of injury from further contact with body tissues. This process also attracts White Blood Cells, called Phagocytes, that consume bacteria and dead or damaged cells.

The role of the innate immune system is to act as the first line of defence from the inside, it reacts to the potentially harmful pathogen within the first few hours of it attacking the system. It is an antigen-independent (non-specific) that has no immunologic memory therefore does not recognise or memorise the same pathogen if the body is then exposed to it in the future. Its primary function is the gathering of immune cells to the site of infection and inflammation by producing cytokines (proteins used for cell to cell communication). Cytokine production leads to the release of antibodies, proteins and glycoproteins, this activates the complement system. The compliment system is a biochemical force that functions to identify and coat foreign antigens, making them open to phagocytosis (cells engulf microbes and remove cell debris). This defence mechanism also clears dead cells, anti-body complexes and removes foreign substances in organs tissues, blood and lymph. It can also activate the adaptive immune response known as antigen presentation.

B.2. The Adapt immune system is the body’s secondary defence mechanism. The adaptive immunity is antigen-dependant and antigen-specific, this means there is a gap in time between exposure to the pathogen and the response. This defence mechanism’s trademark is its capacity for memory which enables the host to a more rapid and efficient immune response. Often the innate immune system activates the adaptive immune system through a process known as antigen presentation. This is where certain cells, i.e. dendritic cells, act as important messengers between the innate and adaptive immune system.

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