B5 - Growth and Development

• A-T AND C-G
• THE BASES ARE ADENINE, CYTOSINE, GUANINE, THYMINE
• EACH SET OF THREE BASES IS THE CODE FOR 1 AMINO ACID
• PROTEINS ARE MADE IN THE CYTOPLASM BY ORGANELLES CALLED RIBOSOMES
• DNA IS TO BIG TO LEAVE THE NUCLEUS
• THE COPY OF DNA IS MADE USING MESSENGER RNA
• MESSENGER RNA IS A SHORTER BUT SINGLE STRAND

HOW THE PROTIENS ARE MADE:

1. THE 2 DNA STRANDS UNZIP. MESSENGER RNA IS MADE USING 1 DNA STRAND AS A TEMPLATE. IT IS A EXACT MATCH.

2. THE MRNA MOVES OUT OF THE NUCLEUS AND JOINS WITH THE RIBOSOME IN THE CYTOPLASM.

3. THE RIBOSOME STICKS THE AMINO ACIDS TOGETHER TO MAKE A CHAIN (PROTIEN), FOLLOWING THE ORDER OF BASES IN THE MRNA.

• CELLS ARE NEEDED FOR GROWTH AND REPAIR
• 1ST THE CELL GROWS AND DUPLICATES ITS CONTENTS. THE NUMBER OF ORGANELLES INCREASES DURING CELL GROWTH. THE CHROMOSOMES ARE COPIED, SO THAT THE CELL HAS 2 COPIES OF ITS DNA
• IT THEN SPLITS IN 2 WITH MITOSIS BY:

1. THE CELL HAS 2 COPIES OF ITS DNA ALL SPREAD OUT IN LONG STRINGS.              

 2, BEFORE THE CELL DIVIDES IT FORMS X SHAPED CHROMOSOMES CALLED CHROMATIDS WHICH ARE JOINED AT THE CENTROMERE.

3. THE CHROMATIDS LINE UP AT THE CENTER OF THE CELL AND THE SPINDLE FIBRES PULL THEM APART.

4.  MEMBRANES FORM AROUND EACH SET OF CHROMOSOMES AND THESE BECOME THE NUCLEI OF THE 2 NEW CELLS. THE CYTOPLASM DIVIDES.

5.  YOU GET 2 NEW CELLS GENETICALLY IDENTICAL TO THE PARENT CELL.

• GAMETES HAVE 1/2 THE USUAL NUMBER OF CHROMOSOMES. DURING REPRODUCTION AN EGG AND SPERM COMBINE TO FORM A NEW CELL - CALLED A ZYGOTE WHICH HAS 46 CHROMOSOMES.
• BODY CELLS HAVE 23 PAIRS OF CHROMOSOMES (46). BUT GAMETES ONLY HAVE 23 SINGLE CHROMOSOMES (23).
• GAMETES ARE PRODUCED BY MEIOSIS AND THIS INVOLVES 2 DIVISIONS. IT PRODUCES CELLS WITH 1/2 THE ORIGINAL NUMBER OF CHROMOSOMES AND HAPPENS IN REPRODUCTIVE ORGANS.
• AS IN MITOSIS THE CELL DUPLICATES ITS DNA BEFORE THE DIVISION AND CHROMATIDS FORM

FIRST DIVISION  -  THE SIMULAR CHROMOSOMES LINE UP IN THE CENTER OF THE CELL  IN PAIRS. THE PAIRS ARE THEN PULLED APART SO EACH NEW CELL HAS ONE COPY OF EACH  CHROMOSOMES. SOME OF THE FATHERS CHROMOSOMES AND SOME OF THE MOTHERS CHROMOSOMES GO INTO EACH CELL. 

SECOND DIVISION -  THE CHROMOSOMES LINE UP IN THE CENTER OF THE EACH CELL. THE SPINDLE FIBRES PULL THE CHROMATIDS APART AND SOME CROSS OVER OCOURS. THE CYTOPLASM DIVIDES AND 4 GAMETES FORM  EACH GAMETE IS GENETICALLY DIFFERENT DUE TO CROSS OVER. MITOSIS CONTINUES TO DUPLICATE THE CELLS.

• A FERTILISED EGG DIVIDES BY MITOSIS TO PRODUCE A BUNDLE OF CELLS. THE CELLS IN THE EMBRYO ARE ALL THE SAME ( EMBRYONIC STEM CELLS) AND ARE UNDIFFERENTIATED. THIS MEANS THEY CAN DIVIDE TO PRODUCE ANY TYPE OF SPECIALISED CELL
• IN HUMANS ALL CELL ARE UNDIFFERENTIATED UP TO THE 8 CELL STAGE. THE PROCESS OF STEM CELLS BECOMING SPECIALISED IS CALLED DIFFERENTIATION . AFTER THE 8 CELL STAGE THE EMBRYO STARTS THIS PROCESS. IT THE START TO DEVELOP TISSUES (GROUPS OF SPECIALISED CELLS) AND ORGANS (GROUPS OF TISSUES).
• ADULTS HAVE STEM CELLS IN BONE MARROW. ADULT STEM CELLS CAN ONLY DIFFERENTIATE INTO CETAIN TYPES OF CELLS
• STEM CELLS CAN SWITCH ON ANY GENE. THE GENES THAT ARE ACTIVE DETERMINE THE TYPE OF CELL THE STEM CELL BECOMES
• ADULT STEM CELLS ARE USED TO CURE DISEASES E.G PEOPLE WITH BLOOD DESEASES CAN HAVE BONE-MARROW TRANSPLANTS.
• EMBRYONIC STEMS CELLS CAN REPLACE FAULTY CELLS IN SICK PEOPLE. TO GET 1 SPECIFIC CELL, SCIENTISTS TRY TO CONTROL DIFFERENTIATION BY ALTERING CONDITIONS TO ACTIVATE GENES. MORE RESEARCH IS NEEDED.
• SOME PEOPLE THINK UNETHICAL AND IT IS REGULATED BY THE GOVERMENT
• CLONING CREATES EMBRYONIC STEM CELLS - THEY ARE CONTROLLED & MAKE SPECIALISED CELLS.

• MERISTEMS CONTAIN PLANT STEM CELLS AND ARE MITOTICALLY ACTIVE. THE MERISTEMS ARE FOUND IN AREAS OF THE PLANT THAT ARE GROWING - ROOTS AND SHOOTS
• THEY PRODUCE UNSPECIALISED CELLS THAT ARE ABLE TO DIVIDE AND FORM ANY CELL TYPE IN THE PLANT. THESE CELLS CAN GENERATE ANY TYPE OF CELL FOR AS LONG AS THEY LIVE.
• THE UNSPECIALISED CELLS CAN BECOME SPECIALISED TO FORM TISSUES LIKE XYLEMM AND PHLOEM
• THESE CAN GROUP TOGETHER TO FORM ORGANS LIKE LEAVES, ROOTS, STEMS AND FLOWERS
• CLONES OF PLANTS ARE PRODUCED BY CUTTINGS. CUTTINGS TAKEN FROM AN AREA IF THE PLANT THATS GROWING WILL CONTAIN MERISTEM CELLS WHICH CAN DIFFERENTIATE TO MAKE ANY CELL.
• A WHOLE NEW PLANT CAN GROW TO MAKE A CLONE OF THE PARENT PLANT. GARDENERS USE CUTTINGS TO MAKE IDENTICAL PLANTS WITH DESIRABLE CARACTERISTICS.
• IF YOU PUT THE CUTTINGS IN THE SOIL THEY WONT ALWAYS GROW. IF YOU ADD ROOTING POWDER WHICH CONTAINS THE GROWTH HORMONE AUXINS THEY WILL PRODUCE ROOTS RAPIDLY AND START GROWING NEW PLANTS.
• THE GROWERS CAN PRODUCE LOTS OF CLONES AND A REALLY GOOD PLANT VERY QUICKLY.

• THE GROWTH TOWARDS OR AWAY FROM LIGHT IS CALLED PHOTOTROPISM & HELPS PLANTS SURVIVE
• SHOOTS ARE POSITIVLY PHOTOTROPIC- THEY GROW TOWARDS LIGHT & ROOTS ARE NEGATIVELY PHOTOTROPIC- THEY GROW AWAY FROM LIGHT
• POSITIVE PHOTOTROPISM - PLANTS NEED SUNLIGHT FOR PHOTOSYNTHESIS AND NEED THIS TO GROWTH AND ENERGY. PHOTOSYNTHESIS OCCOURS MAINLY IN LEAVES SO IT IS IMPORTANT FOR PLANT SHOOTS TO GROW TOWARDS LIGHT
• NEGATIVE PHOTOTROPISM - PLANTS AND NUTRIENTS NEED WATER TO GROW . PHOTOTROPISM MEANS ROOTS GROW AWAY FROM LIGHT, DOWN INTO THE SOIL WHERE THEY CAN ABSORB THE WATER AND NUTRIENTS FOR HEALTHY GROWTH
• AUXINS ARE PLANT, GROWTH HORMONES THAT ARE MADE OF CHEMICALS THAT CONTROL THE GROWTH NEAR THE TIPS OF SHOOTS AND ROOTS. THEY PRODUCE IN THE TIPS AND DIFFUSE BACKWARDS TO STIMULATE CELL ELONGATION PROCESSES. IF THE TIP IS REMOVED THE SHOOT MAY STOP GROWING. AUXINS ARE INVOLVED IN THE PLANTS RESPONSE TO LIGHT, GRAVITY AND WATER.
• WHEN A SHOOT TIP IS EXPOSED TO LIGHT, MORE AUXINS ACCUMULATE ON THE SIDE THATS SHADED THAN THE SIDE IN THE LIGHT. THIS MAKES THE CELL GROW FASTER ON THE SHADED SIDE, SO THE SHOOT GROWS TOWARDS THE LIGHT.