National 4 Biology Unit 2 section 1 Summary notes

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1 National 4 Biology Unit 2 section 1 Summary notes 1. Reproduction For a species to survive it must be able to produce more offspring. Living things can reproduce in different ways asexual reproduction and sexual reproduction. Asexual Reproduction A bacterium reproduces by asexual reproduction. When a bacterium reproduces it simply copies its DNA and then divides in half - we call this process cell division. This means in asexual reproduction there is only one parent and all the offspring are identical to that parent. The diagram below shows asexual reproduction in bacteria. One bacterium divides to form two, which both divide to form four which each divide again to form eight bacteria. Asexual reproduction can grow populations very quickly. Yeast also reproduce by asexual reproduction. You can see yeast reproducing below by forming buds. These buds will eventually form separate but identical cells. Plants can reproduce by asexual reproduction too. They do this by producing structures such as bulbs, plantlets and tubers. Plants can reproduce naturally by asexual reproduction which produces identical offspring. Bulbs are plant s underground food stores which contain side buds to grow into new plants. These bulbs will produce new plants which are genetically identical to the parent. Runners make new plants at the end of long bendy stems e.g. strawberries. Some plants naturally produce miniature version of themselves called plantlets e.g. Mexican hat plants. Plantlet Runner Bulb 1 P a g e

2 Some people use artificial ways of propagating plants. You can take sections of the stem or leaf of a plant, called cuttings, using scissors. After planting the cutting, given the right conditions, they can grow into a whole new plant. Sexual Reproduction Most animals and flowering plants reproduce by what we call sexual reproduction. In sexual reproduction, there are two parents and all the offspring are different from each other. In humans, an egg is produced monthly. Sperm produced in the testicles travel along the sperm duct and are placed in the vagina by the penis. They travel up and fertilise the egg in the oviduct. The fertilised egg then travels to the uterus to grow during pregnancy. In fish, sperm and eggs meet in the water, but the parents leave after and do not look after the young. Different organisms produce different number of eggs. The greater the number of eggs produced, the less their survival chance. This is usually because their level of parental care is less. The DNA in the offspring is a mixture of both parents. Sexual reproduction is very important because it creates variation in the offspring. Variation is important because it create individuals with new combination of genes. These combinations of genes may give the individuals useful characteristics such as resistance to disease, tolerance to drought and other useful characteristics. The more variation there is in a population the more likely it is to be able to be able to survive changes in the environment. Growing plants from seed Plants reproduce by sexual reproduction by using flowers to produce seeds. Pollination happens when the pollen (male sex cell) travels from the anther by insects or the wind to the stigma of another plant. Pollen grows a pollen tube down to the ovary where its nucleus joins with the nucleus of the female sex cell, the ovule. Fertilisation happens and a seed is formed. 2 P a g e

3 2. Commercial uses of plants Plants are grown to provide food, fuel, raw materials, medicines and more. Growers are keen to maximise their yield of plants to maximise their profit. You have already seen how some growers ensure that limiting factors do not inhibit the growth of their plants. Pharming is a new technology which involves genetically engineering plants so that they produce medicinal products. It is hoped that this could eventually be a cheap way to mass produce medicines. It might even be possible to deliver medicines or vaccines in ordinary foods. 3. Growth and development We have looked at how our genes affect the features of living things, however the features of living things are down to more than just their genes. There is another important thing which affects how living things grow and develop which is their environment. Plant seeds need WOW water, oxygen, warmth in order to germinate. The term optimum means the conditions a plant grows best in, e.g. its optimum was at 20 C. Once germination has happened, plants also need sunlight. Any deficiency (lack of) minerals such as nitrogen, phosphorus and potassium or exposure to ultraviolet (UV) light will slow a plant s growth. We don't need to tell you that a balanced diet, water, minerals and vitamins are required for healthy growth and development in humans but you may not know about why these vitamins or food groups are important. Your diet should have a balance between the three main food groups - carbohydrate, protein and fat. Carbohydrates are food such as bread, pasta, rice and potatoes. These are important because they give you energy. Protein is found in foods such as meat, fish, pulses, eggs and tofu. Protein is used to make up the basic framework of the body's tissues and organs. Fat is useful in the body for insulation. It is stored under the skin and keeps us warm. Fat is also important because it helps absorb and carry certain vitamins in the blood. Eating a diet high in saturated fat can lead to high cholesterol levels in the blood which can lead to various cardiovascular diseases. Saturated fat is found in butter, cheese, animal fat. Eating more unsaturated fats can actually lower cholesterol levels in the blood. Unsaturated fats can be found in food like olive oil, oily fish and nuts. 3 P a g e

4 Vitamins and minerals: You should also get plenty of vitamins and minerals by eating at least five portions of fruit and vegetables per day. The table below shows some vitamins and minerals and their function in the body. Vitamin or mineral Vitamin A Vitamin C Vitamin D Foods found in Milk, eggs, liver, carrots. Citrus fruits, peppers, tomatoes, broccoli and spinach. Your skin makes it when you are in the sun! It is also found in egg yolks, oily fish Calcium Milk and other dairy products. Iron Red meat, fish, lentils, beans, green leafy vegetables. Some cereals are also fortified with iron. Function in human body Prevent eye problems. Healthy bones teeth and gums. To absorb calcium (see below) Strong healthy bones Helps red blood cells carry oxygen around the body. 4 P a g e

5 National 5 Biology Unit 2 section 1 Summary notes 1. Cells, tissues and organs Cells whose structure is adapted to carry out a specific function are called specialised. For example, red blood cells are a biconcave shape to increase their surface area for carrying oxygen. A tissue is a group of cells that are specialised to perform a particular function. For example, muscle cells join together to form muscle tissue which contracts to allow movement of our skeleton. Groups of tissues joining together to perform the same function are called organs. For example, our heart is made up of muscle and nerve tissues. Organs then join up to make organ systems, such as the digestive or respiratory systems. Finally, organ systems join up to make an organism. Plants have specialised cells, tissues, organs and systems too. 2. Stem cells and meristems Cells which are able to divide to create new cells are described as stem cells in animals. These cells divide by mitosis to create new cells. Stem cells cells which are formed immediately after fertilisation, called embryonic stem cells, can divide to produce cells which can go on to become any form of specialised cell. These stem cells are therefore crucial for growth. However, as the animal develops its stem cells become more restricted. Firstly, stem cells are restricted to producing groups of tissues and can eventually be restricted to only one tissue. In a fully grown animal, adult stem cells are restricted to producing cells of a particular tissue. For example, the stem cells which divide to replace your blood cells can only divide to become blood cells. Stem cells therefore are crucial for repair. Arguments for stem cells include their many potential medical uses such as growing new organs / tissues for transplant, producing blood for transfusions and as an alternative to animal drug testing. Arguments against often focus on the killing of an embryo when stem cells are extracted which could be seen as taking a life. Plants grow by a combination of cell division (mitosis) and cell elongation. Cell division in plants only occurs at meristems. Meristems can be found at the root and shoot tips which allows the stem and root to lengthen and also between xylem and phloem cells. Meristems divide to form unspecialised cells which can then become any specialised type of plant cell. 5 P a g e

6 3. Reproduction You already know that chromosomes consist of DNA which carries our genetic information. But in order for a species to be successful, this genetic information needs to be passed onto future generations. The vast majority of cells in a multicellular organism can be described as diploid. A diploid cell contains two copies of each of the chromosomes for that species. For example, a healthy human cell consists of 23 different chromosomes. A diploid human cell therefore has 46 chromosomes, or 23 pairs: In order for sexual reproduction to occur, two cells must fuse to form the new individual. If two diploid cells were to fuse the number of chromosomes in the offspring would be double that of the parents. For most species, particularly animal species, this would be fatal. Multicellular organisms therefore need to reduce the chromosome complement of the cells involved in sexual reproduction by half. Cells which have only one set of the species' chromosomes are described as being haploid. In humans these haploid cells are egg and sperm cells, but they are pollen and ovule in plants. Collectively, these types of cells are known as gametes. During sexual reproduction, two haploid gametes fuse to form a new individual. This process is known as fertilisation and the new cell called a zygote contains two sets of chromosomes. It is described as being diploid. This process is summarised in the diagram below. To simplify the diagram, the diploid number in the diagram is 4 and the haploid number is 2. In reality, in humans this is 46 and P a g e

7 Reproduction in plants There are many different types of plants and a great variety of methods of reproduction in the plant kingdom. Many plants can reproduce asexually, but many can also reproduce sexually. In order to reproduce sexually plants will need to produce haploid gametes which can fuse to form a diploid zygote. The organ of sexual reproduction for many plants is the flower. (male) (female) Structure petals anther filament stigma style ovary sepal Function attract insects for pollination produces male gamete (pollen) stalk on which the anther sits sticky, pollen lands here connects stigma and ovary produces female gamete (ovules) protects bud Pollen produced in the anthers are dispersed either by the wind or insects in a process called pollination. Once a pollen grain lands on the stigma of a flower the pollen grows a pollen tube which carries the pollen down the style in to the ovary where it fuses with an ovule through fertilisation to form a diploid zygote. This diploid zygote then develops into a seed which is then dispersed from the plant by various methods. These methods include being eaten by animals (animal internal), stuck to animals coats (animal external) or being spread by the wind. This avoids the offspring competing with the parent plant for resources. 7 P a g e

8 Reproduction in animals In animals, the haploid gametes in animals are egg cells produced by the ovaries and sperm cells produced by the testicles. When females reach puberty, they begin the process of releasing their own eggs, known as ovulation, normally at the rate of one per month. If sperm cells are present during or soon after ovulation, they travel up from the vagina then fertilisation can occur in the fallopian tubes (also called the oviduct) to form a diploid cell. This diploid cell, correctly called a zygote, will start to divide and grow as it travels down and implants into the uterus where it will stay during pregnancy. The uterus lining therefore thickens during the process of ovulation in preparation for pregnancy. If pregnancy is not achieved following ovulation, the lining of the uterus wall breaks down and is released from the body via the vagina - this is what is known as menstruation or "periods". 4. Effects of lifestyle choices Eating too much salt in your diet increases your blood pressure which in turn increases your likelihood of suffering a heart attack. Blood pressure which may be measured using a blood pressure meter. Eating too many fatty foods may lead to obesity, which may lead to an increased likelihood of suffering a heart attack and possibly cancer. Obesity may be measured by calculating a body mass index (BMI). Eating too many sugary foods / drinks can increase likelihood of suffering from type 2 diabetes. Diabetes may be confirmed by testing for glucose in the urine. 8 P a g e

9 Moderate exercise will increase pulse and breathing rates and can reduce the likelihood of developing obesity and diabetes. It can also combat mental health by reducing stress. All illnesses could be treated under the NHS which would reduce death rates and development of certain diseases in Scotland however would mean an increase in taxes. 9 P a g e