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Cells & Heredity Unit- The Cell Cycle • Cells pass through different stages in their life cycle. • The cell cycle starts when a cell is ___________ and ends when the cell ___________ to make new cells. • Before division, the cell makes a copy of its ________ that is stored in its chromosomes. • Prokaryotic and Eukaryotic cells have different processes for cell division. ★ Prokaryotic Cell Cycle and Division • Prokaryotes are a _________ cell with no organelles and their DNA is found on one __________________ chromosome. • Prokaryote cells ___________ using a simple process called binary fission. • Steps: • DNA is _______________ • Cell ___________ and splits in half • End result= 2 _______________ cells ★ Eukaryotic Cell Cycle & Division • Cell division is more ______________ in eukaryotic cells. • Occurs in 3 stages 1. Interphase- DNA ____________ 2. Mitosis- Nucleus ______________ 3. Cytokinesis- Cytoplasm ____________ and the cell divides ★ Interphase- the ______________ stage of the cell cycle 1. Growth phase 1 (G1) • The cell ____________ rapidly • Duplicates its ______________ • Cell spends ___________ of its lifetime in this phase 2. Synthesis phase (S) • The cell copies its ______. This is DNA replication. This makes a copy of each _________________. • The 2 copies are called __________ chromatids and attach at a ____________ point called the centromere. 3. Growth phase 2 (G2) • The cell ____________ more and gets ready to divide. ★ Mitosis • division of the ____________ including the chromosomes • occurs in ____________ phases • produces 2 genetically ______________ cells ★ Prophase- Prepare • Sister _______________ have formed • The nuclear ______________ breaks down • Fibers called ____________ form to help the chromatids move. ★ Metaphase- Middle • Sister chromatids line up in the _____________ of the cell ★ Anaphase- Away • Spindle fibers ________ the sister chromatids toward the opposite poles of the cell. • This gives each pole a complete set of _______________. ★ Telophase- Two nuclei • The chromosomes _______________ • New nuclear _________________ form ★ Cytokinesis- when the cell ______________ • This stage overlaps with the last step in mitosis, telophase. • The cytoplasm _______________ • In animal cells- a cleavage ____________ forms and separates the daughter cells • In plant cells- a cell __________ divides the cell walls of the daughter cells ★ Cell Feedback • Cell cycle is controlled by ________________. • When the cell is ___________ and healthy, the proteins in the cell get a “green light” and the cell starts to copy its organelles and chromosomes. • If there is a DNA ________________, the proteins that control cell division may not control the cell properly. • This can cause Cancer- uncontrolled ______________ of cells. • DNA mutations can cause cells to speed up the cell ___________ or cause cells to never stop dividing. ★ Reproduction • Reproduction is how organisms produce ______________. • There are two types of reproduction: _____________ or _______________ ★ Chromosomes • • A chromosome consists of DNA and protein molecules coiled together. • _______________ shape in prokaryotes • ________________ shape in eukaryotes Humans have ___________ pairs of chromosomes. The last pair determine our ______. • XX = _____________ • XY = _____________ ★ Asexual Reproduction • Asexual reproduction is simpler than sexual reproduction. • It involves just one ______________. • The offspring are genetically ______________ to each other and to the parent. • All __________________ and some eukaryotes reproduce this way. • There are several different methods of asexual reproduction including binary fission, fragmentation, and budding. ★ Binary fission • occurs when a parent cell simply ___________ into two daughter cells • ___________ reproduce this way ★ Fragmentation • occurs when a _______________ breaks off from a parent organism • the piece develops into a new organism • ______________ can reproduce this way ★ Budding • occurs when a parent cell forms a ____________________ bud • the bud stays attached to the parent while it ______________ and develops • it ______________ away from the parent only after it is fully formed • _______ can reproduce this way ★ Sexual reproduction • Is more complicated • It involves two ____________ • Special cells called gametes (sex cells) are produced by the parents that have ___________ of the chromosomes. • In humans, a gamete produced by a _____________ parent is called an egg, while a gamete produced by a ____________ parent is called a sperm. • An offspring forms when two gametes _____________. • The union of the two _____________ is called fertilization. • The ____________ cell that forms when two gametes unite is called a zygote. ★ Chromosome Numbers • In species with sexual reproduction, each ____ cell has two copies of each chromosome. • • The number of ___________ types of chromosomes is called the haploid number. • • Ex: human beings have 23 different chromosomes. Each body cell contains two of each chromosome, for a total of 46 chromosomes. In humans, the haploid number is _______. The number of chromosomes in normal ________ cells is called the diploid number. The diploid number is twice the haploid number. • In humans, the diploid number is two times 23, or _______. ★ Homologous Chromosomes • The two members of a given pair of chromosomes are called homologous chromosomes. • We get one of each homologous pair, or 23 chromosomes, from our ___________. We get the other one of each pair, or 23 chromosomes, from our ____________. • A gamete must have the _________ number of chromosomes. That way, when two gametes unite, the zygote will have the ____________ number. • How are haploid cells produced? The answer is ___________. ★ Meiosis • Meiosis is a special type of cell division that produces ____________ (sex cells). • It produces haploid __________ cells. • Cells prepare for meiosis by replicating their __________. • Next they go through ___________ divisions, meiosis I and meiosis II. • Meiosis I and meiosis II each have ___________ phases: prophase, metaphase, anaphase, and telophase. • This results in _________ haploid daughter cells. ★ Advantage of Asexual Reproduction • Asexual reproduction can happen very _____________. • Under ideal conditions, 100 bacteria can divide to produce millions of bacteria in just a few hours! • Most bacteria don’t live under ideal conditions. Even so, rapid reproduction may allow asexual organisms to be very successful. • They may crowd out other species that reproduce more slowly. ★ Advantages of Sexual Reproduction • Sexual reproduction is typically ________. However, it also has an advantage. Sexual reproduction results in offspring that are all ______________ different. This can be a big plus for a species. The ______________ may help it adapt to changes in the environment. • How does genetic variation arise during sexual reproduction? It happens in three ways: crossing over, independent assortment, and the random union of gametes. • Crossing over occurs during prophase of meiosis I. The paired chromosomes exchange bits of DNA. This _____________ their genetic material. • Independent assortment occurs during metaphase of meiosis I. Chromosomes line up ______________ and which ones end up together at each pole is a matter of chance. • The union of gametes occurs _____________. In sexual reproduction, two gametes unite to produce an offspring. Which two gametes is a matter of chance. Due to these sources of variation, each human couple has the potential to produce more than 64 trillion unique offspring. No wonder we are all different!